Originally Posted by option94
Wirelessly posted (Cingular 7130c: BlackBerry7130/4.1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102)
No. You can't IMM someone with a different I'm service. MSN needs MSN, yahoo needs yahoo, AIM needs AIM.
as Pizzle points out, in the PC world, you can IM persons on Windows Live Messenger (MSN Messenger) from Yahoo Messenger and vice versa, provided you both have the latest versions of clients from the respective company and you have signed up for the beta (usually done from within the client - on Yahoo, its in the form of a hint, and in Live, the link is available when you try to add a new buddy; requires a restart of the client).
also, if your company is federated for IM services with Microsoft LCS, then Office Communicator supposedly works perfectly for all services. we'll have our federation completed in the next few weeks and I'll test it out from the Enterprise Messenger client (although I'm doubtful it will work, but who knows).