Let the hive mind of Engadget get that for you.
"I just switched to Sprint from Verizon about three months ago for the Pre. Then I went for the Hero about a week ago. Now, I miss my hardware keyboard and am thinking about switching to the Moment. I am still able to switch back to Verizon if I want and get the Droid when it arrives. Should I just trade up to the Moment when it comes out, see if I like it, and if not switch to the Droid? Or something else entirely? Help!"
Well, this sounds like a shady way of doing billiing in the first place! Why can't you get payment directly from your customers in the first place, like a typical retailer/service outfit?
This entire mechanism of billing through the phone carrier is too insecure, too rife with crooks, and waaaaayyyy too open for "cramming".
-tor