Due to the wonders of politics, and open communication, allies can communicate with each other through the use of the 'allies' channel. All of your guild's allies will be able to see messages posted to this channel.
If you wish to see which of your guild's allies are online, type “allies”.
If you wish to send a message to your allies, use “allies <blah>”, where blah is the message you wish to send.
If your allies bore you, or you just don't want to listen to them anymore, you could PK a member of each guild you are allied with, removing the guilds from your channel quickly, or, more civilly, you can type “allies -off”.
For more information, read 'help politics', or talk to one of your guild's ranking guild members.