Posted from my CrackBerry at wapforums.crackberry.com
It depends on what your calling plan is. If you are on an America's Choice or a Nationwide plan, you will not incur any roaming charges anywhere in the U.S. including Hawaii or Alaska (verbatim from my call center career).
Most plans have no roaming charges for most carriers. (at least domestic). You would have to call your carrier. What is going to be the most affected by roaming are some services