Gavin
If your circuit consists of 2 T1s then you should have 3 Mb inbound and have 3 Mb outbound. Some people will say that this is 6Mb total bandwidth. Technically that is an accurate statement about total bandwidth. But many people would be likely to not understand it that way.
In practical terms we usually describe bandwidth in uni-directional terms which describe the capacity to move data in one direction.
HTH
Rick
HTH
Rick