I think I read somewhere that Bitcoin addresses can only start with 1, and the feature for addresses starting with 3 has not been developed yet.
It has been developed and in place for quite a while.
Multisignature addresses on the main network always start with a 3. They can be used to give more than one person control over the spending out from that address. Example: any 3 people, from a total of 5, would have to agree in order to spend the coins stored at that address. I believe that's the case in this instance, although in general it can be "any N people out of M".