What is you PSTN connection? PRI? SIP? This is a vital piece of information.
If you have a SIP trunk, you might be running into the new toll fraud prevention feature:
https://supportforums.cisco.com/docs/DOC-12228
If that's the case, you just need to add the necessary IP addresses in the trust list.
If this is not the issue, you will need to provide some debugs. Once you indicate what your call flow is, we can tell you what debugs are needed.
FYI...csim start is not the best way to troubleshoot call failure, as it does not process the entire call flow.