Yeah, don't buy a phone plan! You should be able to get data only, no? I know other carriers do this but if Sprint doesn't, you can check with them to see if they can provision the phone in such a way that voice calls are not allowed. If none of that is possible, one solution *may* be removing the phone module from the BB manually. I've never done this but I'm sure someone has. You shouldn't need to do that though because I would think you can get a data only plan with Sprint and it would not have the ability to make calls.
I do have another idea though...if you have one CAL, you can activate each of the BB's (one at a time) to the BES and then send the IT policy that disables the phone and whatever else you want to restrict, and then remove the account from the BES. The IT policy will stay after the phone is removed from the BES. You could keep activating different BB's on the same account one at a time and do this. If you disable PIM sync and backup for this account, the enterprise activation will be much faster and it won't mess with importing contacts or backing up the settings/data on the devices.
BES 4.1.6 Exchange 2003 SP2