From my experience with this service, you will not be able to just tell someone that number and they will be able to send sms to you, you have to initiate with them first by sending them an sms from your gtalk.

Since you have never sent me a gtalk sms message to my phone number, if I tried to sms you from my phone I would get a reply that there is no account at that number.

I also do not think there is any guarantee that that will always be YOUR sms number and that it may change at some point and/or be different between you and different parties, but not quite sure about that yet.

All that said, I find this service better than the AIM sms service I had been using.