If i change my number and someone calls my old one will it go to voicemail?

I'm on 02 and have a contract Iphone. I'm asking them if i can change my number but if i change it and someone calls my old number will they hear my voicemail or will it say can't be connected etc.

It should say that it can't be connected, unless the phone company screws up somehow. That number is dead for some period before it can be used again and all the services associated with that number are cancelled.

Itll say the.phone number is no longer in service

It will say that the number you have dialed is not in service or something like that

It would say "the number you have called is incorrect" So it wouldn't go to any voicemails. So that wouldn't waste their money who is calling. I think I have helped.

Normally it will say something like
subscriber does not exist, you have misdialed, please check the number you are calling.

The number is now dead. That is the idea.

You can try and pay to keep the old number on a PAYG for example
and that go to voicemail but why change your number if you want people to still call you?