If you are forwarding to your
voip.ms DID and the caller id is important to you it may be possible to see that caller id if you forward the call to
voip.ms as a sip uri call instead of forwarding just to the number. To try this you would need to check X_SpoofCallerID in the ITSP Profile and, of course, format the call as a sip uri call. Be aware, however, that making this X_SpoofCallerID setting could cause problems with other call forwarding or bridging that you may be doing thru the auto attendent.
Voip.ms has a wiki discribing how to format your call to send to them via sip uri.