Can I transfer to a # outside of my Company?
It'll depend on whether you're making or receiving the call. If you receive a call and then need to transfer your caller, you can transfer to a # outside of your Company. You'll just need to make sure that your Admin has enabled this office-wide feature.
If you're making the call and then transferring your caller, you can't transfer to a # outside of your Company.
The # will have to be associated with a Dialpad account, i.e. another Department, Call Queue, Dialpad Team Member, Room Phone, etc.