I am currently trying to extend our metro Ethernet with 1841 routers equipped with a 2mft-t1 card 4esw switch card.
I am trying this using point to point frame relay with separate bridge groups for each Vlan.
Currently the config is working but spanning tree is blocking one of my t1 connections.
But instead you can try out the mfr (multilink FR).
Hope it helps, rate if does