When we receive a call on the PRI GW, the first character is missing on the phone display. This is working fine in SRST. I have set the "Send Extra Leading Character in Display IE" parameter on call manager and I have the first character but extra funny characters at the end.
We saw this when we first migrated our trunks over, but the 'send extra digit' parameter fixed it for us.
However, I have noticed in the past that once in a while I get a call where the first character is still missing. This has always been from Cisco TAC people. Never spent much time troubleshooting it, but I'm guessing the TAC are using Cisco gear of some type.
It would be interesting to find out what might be causing the problem.