Please refer to https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/14SU2/cucm_b_feature-configuration-guide-for-cisco14su2/cucm_mp_se00e358_00_speed-dial-and-abbreviated-dial.html#CUCM_RF_E262225B_00
I suggest that you get rid of the transformations on the gateway. Most people use external phone number masks applied on the phone lines to ensure the correct external numbers are presented to the PSTN.
Check if the outbound diversion header is enabled on the SIP trunk. The most common issue when forwarding external calls back to the PSTN is that the service provider sees a number that doesn't belong to your system originating from it and they rejec...
The upgrade itself and the ISOs is the least of your concerns. Find out if you will be able to migrate your customer's license first.
Also, if you have the ability to open a Cisco TAC case, you can request them to publish the ISOs for you.
