I sent my friend new unlocked blackberry as a holiday gift, she uses it with Rogers (Canada) data only plan. She find out that even with data only plan she got phone number (voice) from Rogers she did not ask for, and charges on such voice plan are truly out of ordinary, like $1/minute for local calls.
I told her to delete phone application from her blackberry which she did, so that neither she accidentally phones from device nor someone can call her. Now she has truly data only blackberry.
She also found that because she still has phone number on it, even without phone software she can receive SMS on blackberry.
Rogers does not charge for up to 2,500 inbound SMS messages, so she has a blackberry that can accept emails, SMS messages but not phone calls. She loves it.