IntegraMOD

I am writing here becouse i know there are some skilled and helpfull people here, so hopefully you can help me with this.

I am working on a site for the game Guild Wars, its a Nordic Ladder where guilds can challenge each other.
We have made a system where guilds can challenge each other on the site and dont have to write "i want to challange you" on the forum. No they can just click on a guild and say challenge, and then the other guild have to confirm it.

My problem is, i would like to make it so when A sends challenge to B, B also recieve an PM on the user he has on the forum.
At the moment we have done it so it sends and email to B, but i would really like to make a PM system that works together with the PM system on phpBB.

In other words, i want to make a system so a user (the guild) outside of the phpBB forum can send a PM to a user (contact person in the other guild) in the phpBB forum when the guild challenge his guild.

But how do i do this, can it be done ?

I am running a clean phpBB forum.

If i havnt made myself clear im sorry, please let me know.
I hope some of you can help me.