If you are using BB10 OS (so using a device such as the Z10, Q10, Q5, Z3, Z30...), version 10.2.1.xxxx, BBM doesn't work on mobile data via 2degrees. It will however work if you're on WiFi.
This includes being being connected via WiFi to a mobile hotspot on 2degrees mobile data. If you are with the other big two telcos, including Skinny, BBM works on their mobile data directly, both prepay and on-account (no special BIS connection with "blackberry.net" APN required).
Note that while BBM doesn't work on 2degrees data (APN: internet), everything else such as email, Facebook and web browser works as you'd expect.
If you're using the Android version of BBM, however, it works just fine on 2degrees mobile data!
It's a similar scenario worldwide with other smaller providers, but as far as I'm aware they are all virtual operators (which 2degrees is not). Hopefully someday BBM on BB10 OS will work on 2degrees (it doesn't seem to be any technical reason why it shouldn't?) but until then, I think I may have to switch providers, or set up a secondary device as a mobile hotspot permanently on a second 2degrees SIM (which is silly - I must really like 2degrees A LOT to even consider doing this).