Number portability question

[SexyK]

Hey everyone - quick question that you may be able to help out with. Does anyone know if there's a time limit for porting a number to a new service provider? For example, if I have a number on a verizon cell phone, and get new service from tmobile with a new number, can I move my verizon number over to the tmobile phone at a later date and abandon the number that tmobile assigned me? Let me know if the question is confusing, haha. I'm just looking at switching to tmobile but my verizon contract doesnt end for two weeks so I don't want to port my number over until the contract ends to avoide cancellation fees. Thanks for any help you all can offer.