[au_kitkat]

And I'm sure there's probably 10,000 threads about this already, so..sorry.

But I was wondering what kind of options there are for a messenger system?

I've heard of JiveTalk and a few others.
But do ALL of them use MediaNet? Or is there one that uses SMS messages?

[Shooperman]

The Blackberry Messenger that comes on the phone is only for Blackberry to Blackberry. As you mentioned, JiveTalk is known to be the best. It's not free, but it is well worth it and uses data not SMS. There are plenty of options out there that use data or SMS, some are free and some you have to pay for, but if you have unlimited data, just get JiveTalk. You won't be disappointed.