Yes, you can continue to use protocol version 7. Note however that you might receive new Calltypes over what you received for in ICM 6. Calltype additions are not considered a change to the protocol, since they are values.

For changes in the protocol between version 6 and 14 or 15, see the version 15 or 16 protocol guide on CDN here http://developer.cisco.com/web/ctisp/documentation

There is an Appendix that lists the protocol changes between versions, so you can accumulate them into what you would need to add to your application to use the newer protocol.

Yes you can use protocol 6 with ICM 8.5 You specify the version you want to use in the OPEN_REQ.