So, I know how to send an text message via Yahoo Messenger on my PC, but how do I do it via Yahoo Messenger Mobile?

I saw a thread stating that you do it via AIM by sending an IM to the phone number like +12125555555. This doesn't seem to be the same in Yahoo Messenger. I've tried like this by choosing "Send Message To.." on the menu and using a number in that format, but that doesn't seem to be the answer.

What is the correct method with Yahoo Messenger Mobile.

Thanks.