In the lab I have a CUCM 7.x system successfully integrated with E2K7SP1.
The SIP Trunk is using TCP (not TLS) and works if I code the IP or the FQDN of the E2K7 UM node.
If I create a SRV record in MS DNS with a priority/weight of 0/0, a port of 5060, and point it at the same A record FQDN as used above I cannot get CUCM to successfully use the SRV.
A nslookup from another client using the same DNS server returns the right results.
"A" record exchange.lab.local = 192.168.2.100
SRV record _sipe2k7._tcp.lab.local is given a weight of 0, a priority of 0, a port of 5060, and is associated to the "A" record of exchange.lab.local.
On the SIP trunk that is working using an IP of 192.168.2.100 or a DNS name of exchange.lab.local, I enter the SRV record of _sipe2k7._tcp.lab.local, check the checkbox for SRV, watch the port automatically change to 0, save, apply, and reset the trunk, and the trunk is no longer usable.