We got our home landline ported over to OPTUS last week it took 2 minutes.
The ADSL2 light went out.
I swapped to the VDSL NBN modem
The INTERNET light came on followed by the phone light.
The only thing I have done is get the phone Caller ID activated and it all worked ok until we got slow downs and a drop out.
if you had DIAL UP you can port.
if you had VOIP maybe Southern own the number like we had with MyNetphone a 5500 number which we may not have as its theirs.
I cant help you if you were VOIP, but if you were dial up it was your number and it should have been ported across.