In general you're better off getting a Mexican cellphone (mobile phone) if you expect anybody local will need to call you. A US cellphone is really only useful if you're a short-term visitor, or to use in addition to your Mexican phone.

In this article, I'll cover each US cellphone carrier in turn, and then carriers from other countries.

(updated on 2010-Feb-11 to mention that AT&T's Go Phone can call Canada - as well as the US - for 25c/min from Mexico).

Verizon and Sprint

Verizon and Sprint (and resellers like Virgin Mobile and PagePlus) use a technology called CDMA. The only Mexican phone company that uses similar technology is IUSAcell.

Verizon and Sprint use (roam on) the ISAcell network when in Mexicali and other big cities, with a 99c/min roaming surcharge.

However, currently IUSAcell do not have any coverage in San Felipe (no tower near here). So, Verizon and Sprint will not work in San Felipe - there is no compatible carrier for them to roam on.

The Verizon web site does list roaming coverage (via IUSAcell) in San Felipe, but that's a different city on the mainland, not this San Felipe.

Maybe IUSAcell will extend coverage to (this) San Felipe in the future. Or maybe not.

Nextel

Nextel, and resellers like Boost, use another technology called iDEN. There is a Mexican Nextel that uses the same technology, and the US Nextel can roam on it when in Mexico.

Like IUSAcell, the Mexican Nextel does not cover San Felipe, and it's even less likely they will extend coverage to here as iDEN is a dying technology. So, Nextel will not work in San Felipe.

Tracfone

Tracfone, and their other brands like Net10, are US prepaid services sold in places like Walmart with highly customized phones.

Even though Tracfone is owned by Carlos Slim, owner of Telcel, Telmex etc. in Mexico, their phones do NOT roam in San Felipe. Some of their phones (mainly Net10) are CDMA (like Verizon and Sprint), some are GSM, but neither have any roaming agreements or billing structure in place to be usable in San Felipe.

AT&T

AT&T, T-Mobile, and some regional US carriers use the world-standard GSM technology.

The two main mobile phone companies in Mexico are Telcel and Movistar. Both also use the world-standard GSM.

Both have excellent coverage in San Felipe, and operate on the GSM 1900MHz band, the same as AT&T and T-mobile. So the technology is fine - your US phone from AT&T and T-Mobile will pick up a signal from them, and be able to roam on their networks, if your account allows it.

Whether your account allows it, and how much it charges, varies a great deal.

AT&T Prepaid

The prepaid (pay as you go) AT&T Go Phone account is unique. It's a US prepaid account that also roams in Mexico, at very reasonable rates. When you're in Mexico, you can use either Telcel's or Movistar's network (whichever has better reception), to make calls to the US (and Canada) at 25c/min and to receive calls on your US number at the same rate. This is identical to the rates when in the US, if you get the $.25 Simple Plan. The lower rates on the pay-per-day plans are not available while roaming in Mexico, and texting and data costs more.

For a very simple, low usage, pre-paid phone account that works (in English) on both sides of the border with a US number and maximum coverage in Mexico it currently can't be beaten. Costs a minimum of $8.33 a month to run, if you reload it with $25 (100 minutes) every three months or $100 each year.

Note: I've heard that the AT&T prepaid will only roam on Telcel, not Movistar (postpaid contracts work on both). Can anybody confirm or deny this? In this area, it makes little difference.

AT&T Plans (contracts)

AT&T has a variety of plans and add-ons that can bring down the cost of roaming in Mexico.

If you don't add anything at all to a standard AT&T voice plan, the roaming surcharge is generally 99c/min, on top of airtime, while roaming on Telcel or Movistar in San Felipe.

The "AT&T Mexico" add-on to a voice plan ($4.99/mo) brings this down to 59c/min. It saves you money if you have 13 or more minutes of phone calls in Mexico each month on average. The AT&T World Traveler add-on ($5.99) also gives you the 59c rate, plus discounts while roaming in other countries like Canada.

For those who expect to use a US phone heavily in Mexico, they have the AT&T Viva Mexico Plans. From $55 a month (plus fees) for 450 anytime minutes and 1000 night/weekend minutes that you can use in both the US and Mexico. Additional minutes are 45c in both countries. There are even more expensive plans with more anytime minutes (but all have only 1000 night/weekend minutes), all the way up to over $200 a month.

There were some older plans on AT&T such as the "North America Plan" which were great value, but they are no longer available for new customers.

Any unlimited data iPhone plan from AT&T does NOT include unlimited data in Mexico.

T-Mobile

Like AT&T, T-Mobile uses GSM and in a similar way roams on both Telcel and Movistar, so has exactly the same coverage. The cost of roaming is the same for both prepaid and postpaid, and there are no special deals, plans or packets.

T-Mobile prepaid

Prepaid is currently $1.49 a minute (on top of airtime) to receive or make phone calls while in Mexico, and 35c to send a text.

T-Mobile plans (contracts)

For T-Mobile plans, you will need to contact them to activate "WorldClass international service" before travel (free). You will then be able to make and receive calls roaming on both Telcel and Movistar for $1.49 a minute plus airtime, 35c to send a text, 20c to receive a text. I'm not aware of any plans or bundles that can reduce these rates.

So, T-Mobile will work, but it's expensive. Note that the Google Nexus One phone on T-Mobile does NOT have the 850 3G band needed in Mexico. It will not work at 3G speeds in San Felipe, and any data bundles included in it do NOT include any data in Mexico.

Other US carriers

If your US phone is with a minor or regional carrier in the US, whether you will get any signal in San Felipe depends on the technology they use, and whether you can actually use it depends on whether they have a roaming agreement with Telcel or Movistar - some small companies may not.

In general, if it's a CDMA carrier (the phone has an ESN number), you won't have any service. If it's a GSM carrier (the phone has a sim card inside), you might have coverage if you're on a plan, not prepaid. You'll need to contact the carrier for exact details - be sure to ask them about costs when you USE the phone in Mexico, rather than when you CALL Mexico. If it does work, it'll probably be one or two dollars a minute for roaming, and will likely need to be activated before you arrive.

If you do have information on a regional carrier from the USA that roams OK in San Felipe, please add a comment below this article and I'll update this section.

Canadian Cellphones

The cellphone market in Canada is changing rapidly with a lot of new carriers, and new technology. None of these have yet produced affordable roaming in Mexico on a Canadian phone.

Rogers and Fido

The current main GSM carrier is Rogers/Fido. Their (older) GSM 1900 technology and contract plans will roam on both Telcel and Movistar in San Felipe, for C$3 per minute both incoming and outgoing, and 75c to send a text. They also offer the "CALA (Caribbean & Latin America) Voice Travel Pack" of minutes that can bring the roaming rate down to as low as C$1.29 a minute when you buy a package in advance (minutes have to be used within one month).

Rogers and Fido pay-as-you-go prepaid do not work in Mexico.

Bell

The legacy EV-DO phones from Bell will not work in San Felipe. The newer UTMS (and GSM) phones will, including with 3G if the phone supports the right band. It's C$2.99/min to receive or make a call. Like Rogers and Fido, there is no roaming with prepaid.

Telus

Like Bell, only the newer technology phones from Telus will roam in San Felipe, and again no prepaid. As seems be standard amongst Canadian carriers, it's C$3 to receive or make a call. For C$10 there is is a "Voice Pass" that reduces to roaming cost to $2.25/min for 30 days.

Other Carriers

The many other new carriers in Canada like Wind and Dave are introducing mostly GSM and 3G phones that may work in Mexico in the future (some will not as they are on the wrong bands). At present most do not offer roaming in Mexico, but this is something that will evolve during 2010 and I'll update this when information is available.

Another option for Canadians is to get an AT&T Go Phone (see the US section above). Calls to Canada from Mexico are just 25c/min. Most people calling you from Canada can probably call the US number of the Go Phone for the same cost as calling a Canadian phone, and it'll cost you 25c (US) a minute to receive.

Mobile Phones from Other Countries

Mobile phones from most countries of the world will work in San Felipe, roaming on Telcel or Movistar, providing the phone is a GSM tri-band or quad-band phone (has the 1900MHz band, same as you need for the US).

3G phones with the 2100 band used in Europe and Asia will not work (on 3G) in San Felipe. Mexico uses the 3G 850 band (some phones from Telstra Australia and Telecom NZ have this band).

In many cases you will need a postpaid (contract) account, rather than prepaid, although roaming with prepaid is improving all the time.

The roaming costs are way too expensive for anything other than emergency use. I'm not aware of any non-US carrier that has affordable (under $1/min) roaming in Mexico.

For example Orange (UK) charge £1.00/min to receive a call, £1.75 (US$2.80) to make a call, and 50p to send a text, for both pay monthly and pay as you go. T-Mobil (Germany) charge 1,79 € incoming and a very pricey 2,99 € (US$4.33) per minute outgoing.

So it makes a lot of sense to get a local SIM from Telcel or Movistar if your phone account is from a country other than the US and you plan to make calls in Mexico. If you're mainly receiving calls it's a tougher decision, as it can be expensive for others to call your Mexican mobile, possibly almost as much as you would pay to roam.

Unlimited Data

I've focused on voice calls in this article, as data is another whole subject. But, a warning. If your phone plan includes "unlimited data", that does NOT apply in Mexico, regardless of what any customer service person tells you. There is no unlimited data package from the US that includes unlimited data outside the US. None. No unlimited nights and weekends for voice calls either, of course, even if you have that in the US.

When in Mexico when you use data with your foreign phone you will be charged roaming rates, which are very high. It is entirely possible to run up a bill of hundreds, or thousands, of dollars for the data while watching a TV program on your iPhone. You can even run up a sizable bill with automated email checking or automated updates. To avoid the risk, when outside the US disable the data features on your phone except for a short time while you really need it, such as to check email.

Making a call

I haven't yet covered actually making a call with the US phone while in Mexico.

You are not on a US phone network (even if the phone says AT&T), you are roaming on a Mexican network and have to dial as dialled from Mexico. To call the US or Canada, dial 001 or +1 for North America, then the area code and number.

Other ways to receive calls

One of the arguments some use for keeping a US cellphone in Mexico is to be easily reachable on a US number. There are much better ways to do this, including internet phones and forwarding, which can be cheap or even free, which I'll go into later in another article.

Other plans and rates

If you're aware of any other currently available plans and rates for using US or Canadian cellphones in Mexico, or changes to or errors in the above, do leave a comment below so I can keep it up to date! Thank you.