You best option for communication to the states is a Google Voice account found here: www.google.com/voice . With this you have to create a google account and sign up for an account in the US. After creating an account, you will now have the ability to phone any US or Canada phone for free over the internet. Most places in Costa Rica have free internet for their guests in the restuarants, etc. Bring your laptop and some earphones!
We have Ooma Service for our VOIP and it works fantastic but with this you need to have a hard line to connect the service through provided equipment. If you live here then this is an option for you. Travelers use Google Voice.
US/Canada Cell Phones:
BE AWARE OF YOUR CHARGES!! It will cost you big money when you are here for your stay. We urge you to turn your phone off and the data service!!!! Airplane mode is your best bet here and then use your wifi for smartphones.