Surprisingly, as of 2011.12.27, Verizon does not allow you to cancel your wireless cell phone service via their website. If you try to contact them about canceling your account, you will receive the following message:

If you wish to cancel your service, you will need to speak to someone at Customer Service.

Please call us at 1-800-922-0204 and press prompt 4.

So, to cancel service your best bet will probably be to call that number!