Well I would act real casual, invite Voice mail for a meal or something and the other party you want to set Voice mail up with… And hope for chemistry if they get along make an excuse and leave.
Or my B answer is
"Call Diverts" (or aka Call Forward ) as in "Call Settings"
VOICE MAIL after either 5, 10, 15, 20, 25, 30 seconds (Just those 6 time intervals can be set )
[Normally eg set to 10 seconds the call is then routed to Voice Mail. Not in you case ]
You cannot amend it to another value you have to cancel it and then SET TO ANOTHER VALUE eg If it were set to 10 seconds you could not amend to 15 seconds you cancel it only then when you set it will those 6 time interval swill appear
So start again "CANCEL ALL" VOICE CALL.
Activate each for the length on time, if you leave it cancelled it will NEVER ever go to VM
So eg setting for "IF NOT ANSWERED" set for 30 second max then DIVERT TO VOICE MAIL
and for the other options if busy etc
30 second is max for all Networks (GSM code)
You are diverting the call after X time to voice mail (or you set it to another number… You'll see)
"However when I call my own number I get a busy tone obviously!"
Were you really busy or?
But seriously you have to go to your network and ask them for the VM number, it is usually just 2 or 3 digits, and that's how you pick up your voice mail, or some phones pre touch screen a long press on key which has a tape cassette symbol dials VM
I do not own any apple products but all the phone I have are as above… So there.