Are you using CUCM or CME?

If you already have the translation pattern configured change the "Called Party Transformations" to extension 156 on that translation pattern. HTH

https://www.cisco.com/c/en/us/td/docs/collaboration/CWMS/2_8/Administration_Guide/cwms_b_cwms-administration-2-8.html If you want to play around with Webex instead of CWMS you can use dcloud or devnet, you can also sign up for a free trail if you go ...

You can do this through the bulk admin.Bulk Administration>Phones>Add/Update Lines>Update Lines