How many IM clients do you have installed on your PC right now? At least two, provided that you don't have an all-in-one IM client, like Trilian, and that's because the rule of thumb is that an Instant Messaging client from one producer cannot be compatible with another one.

So, if you want to talk with your friends who use MSN Messenger, your Yahoo Messenger won't be of service.

But this might change soon, if the two giants, Microsoft and Yahoo, decide (according to the information disclosed by Wall Street Journal) to allow their IM clients to intercommunicate.

This move will surely affect AOL, whose Instant Messaging client, AIM, is currently in the lead. It's unlikely that Google, which introduced in August Google Talk, will suffer from this partnership, their instant messaging client being already far behind the other players.

According to the statistics published by Radicati and quoted by the Wall Street Journal, AOL's IM client is currently used by 56% of the instant messaging users worldwide. Should the information be confirmed, the Yahoo Messenger - MSN Messenger combination would reach 44%.

And since both IM clients have voice capabilities as well, the new alliance would become an even stronger competitor for Skype.