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1. Hardware.
Ensure you also have PVDM (DSP) resources, otherwise your FXO will not be usable (see this at the CLI with a show ver).
2. IP Telephony
Configure your basic telephony. Google this - there are bucketloads of minimal configs on the web.
3. Configure dial-peers for external connectivity.
Google this as well. Best to build these to suit the area you are in.
4. Configure voice interfaces - generally want to use PLAR for an FXO.
voice-port x/x/x
connection plar 3910
That should give you a good high-level start.