The Telcel 3G is available prepaid (pay as you go), or on a monthly contract plan.

The prepaid has a 100MB/day average download limit. So for example for a 30 day prepaid period you can consume up to 3GB in total during that time, more than 100MB some days, less than that other days. The prepaid period ends when the days expire OR when the download limit is reached, whichever happens first (this is a change, before April 2010 it was different).

The contract plan limits vary. There is no unlimited data option on any of them. In most cases, the prepaid price is very comparable to a contract, so there is little reason to get a contract.

These limits rule out heavy use of streaming video, large software downloading etc. as you would consume the data really quickly. But it's fine for most other usage, many times faster than the Telnor wireless alternative. It's very usable for Skype, and proper VOIP (internet phone) providers like Localphone, Vonage and others.

Typical download speeds are over 1Mb/s (one megabit per second) during the day (sometimes half that at really busy times), over 2MB/s at night. Upload speeds are generally around 100-300 Mb/s. So it's comparable to wired DSL. Ping times to the US are around 200mS most of the time, which makes it unsuitable for gaming but is otherwise plenty fast enough for most uses including VPN (virtual private networks). Generally the connection to the internet is routed through Tijuana and then to L.A., sometimes through Sonora to Dallas.

Reliability isn't perfect. There are random days when the connection often drops, you will need to redial when that happens (I've set up my modem to auto-redial so the interuption is rarely more than 30 seconds). Not every day is like that, sometimes the connection is fine for days on end, There are also days when it is excessively slow, although that is usually less than one or two days a month. Downtime has been around half a day every other month. During the April 2010 earthquake it dropped to slower speeds for a few hours but carried on working.

I've written separate articles on the hardware needed for Telcel 3G internet in San Felipe and How to buy data access on Telcel Amigo.