MAP (Mobile application part) would not apply between
carriers most likely. They would likely connect via
basic ansi isup trunks which would strip the MAP info
going to the next switch since it wouldn't be applicable
to the next network.

   hope this helps
   questions@telcosupport.net

http://www.telcosupport.net

Interim Standard 41 (IS-41) was the name of a specification produced by
the TIA/EIA before it was made an ANSI standard, and renamed ANSI-41.
It is now also known as TIA/EIA-41 or ANSI/TIA/EIA-41.  These
specifications define the north American MAP protocol standard.

Roaming between ANSI-41 and GSM networks is achieved through use of a
gateway that converts one MAP protocol to the other, and vice versa.
The TCAP, SCCP, and MTP layers of the stack are also converted by these
gateways.

You may want to obtain a copy of a document called the GSM/ANSI-136
Network Interworking Specification, which was first published back in
1999 by the GSM/ANSI-136 Interoperability Team (GAIT) on behalf of the
Universal Wireless Communications Consortium (UWCC) and North American
GSM Alliance.

Holmespundit