G-Mail forwarding is fine on the BIS. Flawless in my opinion ;)
SMS is not included in this or any blackberry plan. SMS is an add-on that you have to get seperately.
If you use the built in messenger from .. I think it's RIM but maybe it's T-Mo. But yah, if you use that then you will get charged per message based on your SMS add-on plan.
But you can always get 3rd party software like. Verichat (www.verichat.com
) and sign onto msn, aim, icq, and I forget what else it has... but if you use something like that it does not use SMS to message. It's just like a normal chat client via the internet =)