Can you keep your cell phone number
One reason some people stay with one carrier forever is they believe that if they leave, they will loose their long held, and much coveted phone number. Nothing could be further from the truth. In fact, that is probably the last consideration I would have when deciding which cell phone company to go with.
There is actually a federal law known as number portability that says basically that your phone number is yours forever as long as you want to keep it. In fact, if you look on your most recent cell phone bill, there is often a charge "To comply with government mandated programs." If you look close, it sometimes even mentions number portability as one of those programs. So, you are already paying for it whether you know it or not, so why not keep your number?
So, I am going with another provider, what do I need to do? First of all, call the NEW carrier and tell them you want to bring your number over to them. Of course I am assuming you called your old provider first to make sure there are no penalties for early cancellation, etc. So, the new carrier will then check to make sure they can bring your number over (most, but not all numbers are eligible to be moved to every carrier.) Then, they will simply schedule the transfer.
Most transfers only take around a day or two at the most. The number is transferred, and normally the old account is canceled as soon as that happens. Just call your old carrier to make sure, and that there aren't any extra charges such as having to pay for the whole month or some weird early termination fee you never heard of before. Worst case scenario, you can move the number back and most carriers will return your early termination fee if the number is moved back right away. Again, it is better to check before the fact, but some carriers won't be too up front about all those fees until you actually leave, and then they figure they can charge you whatever they want, because you aren't coming back anyway.
Usually the new company will make you open an account, start a temporary number and then replace it with your old number. As soon as your number is moved, the temporary number goes back into the available number pool. It really is a pretty simple process. The new company will take care of contacting the original one, moving the number and getting your new service up and running. All you have to do is start the process.