How to add people to your yahoo messenger list that don't have an account?

I have a ipod touch and recently got the app called yahoo messenger. I am mainly using it for texting to cell phones. I have a few friends that have accounts on yahoo messenger, but many that don't. How would i make my friend show up in my messenger with just a cell number not and not a yahoo id?

How to add people to your yahoo messenger list that don't have an account?
I have the samee problemo. Let me know your solution.