Hi there,
Well the fact still stands that currently there is no 3CX Phone client for Blackberry, but the forum post you linked us to says that some people used a 3rd-party application that runs on Blackberry and registered an extension using that.
This does sound possible as you can manually register most softphone clients, however there is no guarantee the all functions (blind transfer, attended transfer, hold, etc) will work as intended obviously as the software is not developed by 3CX.
If you are an owner of a Blackberry the best way to check if it works or not is to try it. Some people say they have done it, so maybe you could PM one of the users that have allegedly got it running.
Keep in mind though that using 3rd party software and/or non-supported deskphones phones may or may not work, but 3CX Support won't be able to help if you run into any issues.