Quote: "
Could we have the same multipart function of segments for entities??"
Actually what you describe for a telephone box wouldn't be too hard right now Nbt, some time ago even had a working elevator which you could step into, doors open close etc, but to be honest it was an incredible amount of work to get it happening and seriously not worth the effort for most folks.
Myself and s4real spent a lot of our tme on it and built upon xplosys script for pgup/pgdown to move it, cant even remember how many scripts it took but it actually worked.
Put it up for free download so anyone could grab it if they wanted to take it apart, its buried in here somewhere.
Help yourself to looking at it if I remember correctly theres a ready built map so you can just load it straight up, had to do that as placement of the entity's was crucial.
http://forum.thegamecreators.com/?m=forum_view&t=130987&b=24
Now what I think your really asking for is the ability to use polygonal collison on dynamic entity's instead of the default box this would allow for multitexturing too, but problem then is lightmapping, dont know if thats possible or not.