If you use a cell phone, make sure your calling plan matches the pattern of calls you typically make.
Understand peak calling periods, area coverage, roaming, and termination charges.
Contracts offered by most carriers will provide you with a trial period of 14 days or more.
Use that time to make sure the service provides coverage in all the places you will be using the phone (home, work etc.).
Prepaid wireless plans tend to have higher per minute rates and fees but may be a better option if you use the phone only occasionally.