From software 2.13 the option is added to transfer the 2nd Call.
Situation: You are on the phone with a Caller (1020) and have one call on-hold(1030).
Press to put 2nd Call on-hold.
Dial the number, the Call is highlighted that you can transfer when pressing the Transfer button, via Up/Down you can select the other call.
After Call transfer you will be automatic connected with the party that is not transferred.