I was wondering the same thing about outbounding from Service Titan!
Until there is a better solution, the only temporary solution I can think of would be to make one "outbound" account. I have not done this myself, so I don't know the hiccups it would come with. You would have to add a phone number to the account, call it from service titan, then probably delete it from the "outbound" account. Not sure if this is worth the extra work for what you are trying to accomplish, but its the best I could think of other than using another third party soft phone service or a hard/ desk phone.
