Voice over IP is pretty mainstream at this point. I use BabyTel (I am a reseller and make a commission if you use the below links. If you wish to bypass that, simply go to their website)
For Enterprise accounts – Click here
For Residential & Small Business accounts – Click here
You then have a local number so your friends back home can easily reach you.
Some choose the Magic Jack or simply use Skype.
There are plenty of Casa de Cambios around, but a bank always gives you a better rate. I found the American Express places give you a great rate! If you run out of pesos, use pretty much any ATM. The typical fee is about $0.75 per transaction (that is the fee from the local bank. You might get an extra fee from your home bank) but you get a decent rate and you get local currency.
What is the point of coming here if you don’t integrate with the locals? Take some Spanish courses before you come and it will surely help with day to day activities. Most resort towns have English speaking staff, but you never know. You can save a lot if you shop where the locals shop…and that’s in Spanish.