It's possible to create a sip trunk between a CCM 4.x and a UC500 in order to use the CCM as pstn gateway and permit internal voip calls?
- on the CCM configure voip trunk as per documentation
- on the voice GW configure DP so that call to certain numbers (hopefully you've ISDN) can go to CME
- on CME configure a voip DP with destination-pattern the numbers that are on the CCM, ipv4 address and codec g711u. Also configure a destinaion-pattern for PST calls having session target the other GW.
Hope this helps, please rate post if it does!