I'm not seeing that acronym mentioned anywhere on Bell's site. If a data block is applied, this will prevent you from sending and receiving picture messages, (MMS). The data used to send or receive a picture message is not chargeable to you. The problem is that apps that require updates may 'see' the open data connection and update in the background, resulting in a data usage charge.
Programming a separate APN for MMS only, seemed to be a plausible solution at the time. Unfortunately, it only worked for a select few devices. You're welcome to try it, but there are no guarantees this will work for your device, (see Chad's post). http://bit.ly/1MRXxjY Some of the tips in the link below should help to minimize data usage when sending MMS messages.