I'm with Virgin but because they're closing down I'm trying to move across to Optus. There's a plan that I like and I want to sign up but I like my phone number on my Virgin SIM card. Is there any way I can transfer the new Optus plan to the Virgin SIM card and keep my phone number? The SIM card was also in my prepaid phone and I'd like to get a plan now, will this make a difference?
Unless I'm misunderstanding you, what you're referring to is "porting" your number and it's very doable.
Essentially you'll place your order with Optus (online, instore, over the phone etc) and provide them with your phone number, name, date of birth and other details. They'll bring the number over for you and activate your plan. You will need a new SIM card which Optus will provide but otherwise, it should be a relatively straightforward process
You can absolutely keep your number - just let the staff know when you process your order and they'll make sure it is transferred.
You will need to change your physical SIM card when you make the switch to Optus, but be rest assured your phone number itself won't be impacted.
I'd recommend jumping on live chat (http://yesopt.us/chat2us) and asking staff to process your order.
Let us know how you go!