To get the right plan, consider where you intend to use your phone.

Will you call locally? Nationally? Per-minute -- roaming -- charges can add up quickly if you make or receive calls outside your local calling area (which varies by location, but tends to be relatively consistent across carriers).

Corporate rates, usually available if there are at least five phones activated, can help lower your monthly costs.

Plans usually require monthly payments that include a set amount of "free" airtime, which is sometimes divided into "peak" and "off-peak" minutes. (And remember, these minutes are used up whether you're making the calls or receiving them.)

Exceeding this will usually cost you on a per-minute basis, so ideally your plan should bill by the second, not the minute.

Unsure about your usage? Go with a plan that will allow you to switch later on and get billed retroactively at that rate.