@ lhm: Thanks for your input. I could reproduce your example. It seems to work for me with no delay with or without the S0 suffix.
@ HMishra: That's very odd! I cannot see why your changes added to incoming latency. Anyhow the S0 is doing no good there, so best leave it out.
This is not the right thread for an in-depth discussion on DigitMaps and OutboundCallRoutes. I think people sometimes mix the two up. DigitMaps dictate what digits are allowed to be dialled, OutboundCallRoutes decide where the digits will be routed to. (Yes, I know there's a bit more to it than that!) One of the problems here is that if you have an xx. rule or a [^*#]@@. Rule in any DigitMap, then all sorts of numbers can sneak through. This can confuse any testing. I try to ban xx. rules and change [^*#]@@. to [^*#]@@.'@'@@.
Unless you are very expert using DigitMaps etc, I advise people to leave the 911 at default in the Phone Port DigitMap and Phone Port OutboundCallRoutes. I have yet to see any use of S0 that made any difference to 911.
If you are quite expert using DigitMaps etc and using Trunk Groups, then 911 may well be better of in trunk DigitMaps (sp1, sp2 etc), but that's another subject for another thread!
Stay safe – make sure your 911 is working as it should