Need more information ....
what is System type?
What is system version?
How is the extension programmed , is it in a PRG or MDU group?
is sip softphone running locally on Lan or on smart device ?
are you using the MiCollab(UCA Client?) or mod call dialling , fo rmid call dialling with Sip trunks you will need a MBG as sip Proxy
if programmed properly and other group members are present in the group , then yes handoff should work
If I never did anything I'd never done before , I'd never do anything.....