I have a Mikrotik 1100 H2 routerboard and have been asked if it is an SBC router. Can someone answer that question?

If SBC should mean Single Board Computer, then yes, according to the pictures it is built on a single board.
If you actually mean SoC (System on a Chip), then no, the QorIQ P2020 has external RAM and Flash, with a dual core e500v2 architecture on chip.

Why is this relevant?

If SBC should mean Single Board Computer, then yes, according to the pictures it is built on a single board.
If you actually mean SoC (System on a Chip), then no, the QorIQ P2020 has external RAM and Flash, with a dual core e500v2 architecture on chip.

Why is this relevant?

By SBC I meant Session Border Controller. When we contact another company and the call is forwarded, the connection is being dropped. This is what we are being told: "In the initial early offer SIP INVITE we see the SDP media attribute “sendrecv”. This allows voice to pass in both directions. In the SIP 200 OK SDP we see that by not having a media attribute at all it is by default in accepting the “sendrecv” status. Later, when the Promedica PBX goes to transfer the call from the auto attendant they send a SIP INVITE SDP to mark the stream as “inactive” since that stream will not be used again by that particular system. When the Promedica PBX sends out a new SIP INVITE and the Central Travel PBX responds with a late/delayed offer it is not recognizing that as part of RFC 3264 and RFC 6337 it should have used the media attribute “sendrecv” in the SDP. It is instead still using “inactive” which forces the Promedica PBX to also mark the stream as “inactive” and the call is essentially stuck on hold." Our Toshiba support person said: The Toshiba system does not do any media anchoring. This will take an SBC router."

That's the reason for the question.

Well, RouterOS does have an SIP ALG. That does not really turn RouterOS into a real SBC, but may cause some troubles like yours. You can try turning it on or off and see if it helps.

SIP was disabled. I enabled it and began getting reports back that calls were breaking up. I disabled it and the calls were no longer breaking up. It's hard for me to accept that Mikrotik routerboards are not compatible with some PBX phone systems but that's the way it's looking.