i have cucm 12 that is working fine , i recently implemented call pick but it only works with internal calls , if an outside call from pstn comes the button doesn't work? btw it is implemented on phones in a branch connected to us in a site to site vpn
Have you checked the partition of CallPickupGroup and the calling search space of your voicegateway.
Hope this helps
Do you use SIP or SCCP phones?
What is your connection to the PSTN and have you ever debugged your gateway to see what is going on?