Hi,
When you say after the 6th digit, is there a wait for the inter-digit timeout or are you saying it's immediate?
If you have route pattern overlapping with your internal extension - CUCM should wait for interdigit timeout to figure out if you are going to dial any more digits. After that it should figure out your most specific match is the internal extension, and try and send the call there.
Is this happening? do you get a pause before the call gets sent to the extension?
SIP trunk should behave the same, it's not really the trunk or SCCP phone doing the matching in this case, it's the callmanager processes themselves. You can see this in the CCM traces.
Cheers,
Tim