Alltel today announced it has signed MMS interconnection agreements with Cingular Wireless and Verizon Wireless, allowing customers from all three networks to exchange picture and video messages.

The deal is the latest in a slate of individual agreements among the Tier I and Tier II operators allowing the free exchange of MMS across their networks. Carriers have been hooking into the interoperability hubs of Mobile 365 and Verisign’s Lightsurf. So far Alltel, Cingular, Verizon, U.S. Cellular, and Leap Wireless have connected into Mobile 365’s hub, while Sprint, T-Mobile, Dobson Communications and a consortium of Canadian carriers have opted for Lightsurf’s hub.

While all of the carriers may be connected to the same hubs, they aren’t necessarily all interconnected. Carriers have been ironing out individual interconnection agreements with one another before allowing traffic to flow between their networks. There are still some major carriers that have not—at least publicly—entered into interoperability agreement. For instance, Verizon Wireless is connected to Sprint, Cingular but not to T-Mobile, while Cingular is supporting MMS between all of the Tier I operators.