I have just finished a call to AT&T about my phone use in EC and have found out some info on the I Phone I would like to share since this question came up on the forum recently.
According to AT&T you can use your US serviced I phone In Ec paying the roaming charges that are $2.29 per minute.
On the other hand if you want to buy your phone service from a local provider you can't use your US I phone because its not unlockable!
I guess the only way would be to buy a new I phone in EC if the local carriers offer it unless you love it so much that you want to pay $2.29 per minute.
This is information from ATT. If you have an I phone in the US I recommend that you re-check this information before you plan using it.