I like to create an ACL to define what I want to debug/dump in the console. Example:
ip access-list extended sip-capture
permit udp any any eq 5060
Start logging to a text file in your terminal application, then use the following command at the enable prompt to begin the packet dump:
debug ip packet sip-capture dump
undebug all (or just u a)
Stop your text logging and then follow the instructions in the post you mentioned to convert the text log to a PCAP file.
Sometimes it's important to collect data over a long period, but SSH/telnet sessions typically timeout after a few minutes. I found this article helpful to setup persistent debugging over a longer period: Enabling Persistent Debug Logging
I had edited my access list to not capture the correct info. Thanks for the quick and helpful advice.