Phone service in Mexico-Are SIM's available in Ajijic?

As many of you know, my wife and I aare making our initial visit starting next week to Ajijic. My iPhone 4 will not get service down theere and there is no roaming....since it is unlocked I can use a SIM from any carrier, so I wondered are there SIM's available down there so I can get service for a short time, or is it something I should take care of before I leave?
Thanks

Yes you can go into any TelCel store and get a sim card for 150 pesos. You can then load it up with prepaid minutes. Very quick and easy.

Curious why you believe your phone won't work here, all the major carriers work here. Roaming is costly though.

I use H2O on my iPhone which really is an ATT carrier, but only costs me $50 a month with data...no contract. H2O says there is no coverage outside the US...I just believed them, but...since SIM's can be had easlily down there...I'll certainly see if there is coverage first

Good idea. AT&T does work here but maybe something that H2O doesn't allow. Easy to get a SIM here.

Is it a normal SIM card? I was under the impression that the iPhone 4 SIM cards are different than the normal SIM card. I know the iPhone 3gs has a normal SIM, but thought the iPhone 4 was different.