Just in case you wondered (Obviously, I did), I submitted this question to the FCC for legal requirements:
Is it legal for a GMRS station to communicate with an FRS station on the shared (interstitial) channels common to the two services?
Solution Details : Dear Robert,
Yes it is legal for a GMRS station to communicate with an FRS station on the channels shared by the two services. If you are licensed to use GMRS. Please see website http://wireless.fcc.gov/services/index.htm?job=service_home&id=general_mobile for further information.
If you have any further questions, or need additional information, please submit a request through http://esupport.fcc.gov/index.htm or call the ULS Customer Support Hotline at (877) 480-3201 and select option 2 after the main menu recording.
Sincerely,
ULS Customer Support Hotline
Agent 3823
I asked, because the GMRS rules specify that GMRS is to be used to communicate with other GMRS stations. The GMRS rules, of course, are in pretty bad shape, with rules referring to other rule sections that no longer exist, etc…