Just purchased and had installation of UX5000 system and now trying to use the CALL FORWARDING OFF-PREMISE feature which seems pretty straight forward to use... CALL1, *4, 6, #9, mycellnumber, HOLD, SPK ... but when I press the 6 key for type of device all I get is a busy signal and then nothing in the setup continues.

Anyone know what has to be done to allow to use this feature?

You have to have the proper settings in the Class of Service to allow that. I suggest getting the installation company to adjust that.

Coral Tech is right on. The ability to allow trunk-to-trunk transfer for call forwarding off-premise is not enabled by default. You will need to get your installer to go into the system and program it to allow that......

also make sure that transfering on hold to a trunk is adjusted so that you don't accidently start conferencing 2 calls together

Yes, make sure T2T is enabled and if you make sure Unscreened Transfer is select if you are VM picking up.