The process in Ireland is very, very easy and nearly instantaneous.
Confirm its your mobile by sending a text to your phone with a verification code or, in a shop they'll just call you from their landline to confirm it's s you. Once that's done, your phone is ported.
For bill pay you simply give your new operator your mobile number and account number. Once that's done and they've done their credit check on you, your port is competed without any need to call or interact with your old network.
For landlines you just need the UAN number which is at the top of every bill, PSTN, cable, VoIP etc if it's providing a landline number it has a UAN. You give that & your phone number to the new operator, they do a 3rd party verification (if done on the phone) and once done, you're transferred to the new provider,
If you're still in contract your network can a) block the port or b) send you a bill including their early termination fee.
Whole process is automated and it's been like this since about 2001