Ofcom's been thinking about simplifying the process for the best part of two years now. Initially, it floated the idea of "gaining-provider led" switching. This would've meant you only needed to talk to the carrier you wanted to move to, and it would take care of the rest, including cancelling your current contract. Thanks to Ofcom, this is how you go about changing broadband provider these days.
The "gaining-provider led" option is now off the table, as it would've cost the mobile industry an estimated £87 million to implement. In order to minimise costs that could trickle down to the consumer, Ofcom settled on the "auto-switch" process, which will cost less than half as much over ten years. While not quite as convenient, the expanded proposals address the majority of complaints customers have with the existing switching process.
After sending the free text message or doing the equivalent online, your current provider will be required to get back to you immediately with either your PAC code, or what's called a "cancellation code" if you're not fussed about keeping your number. In the same breathe, they'll also notify you of any early exit fees and outstanding device costs you may be on the hook for, or remind you of your remaining credit balance if you're on pay-as-you-go.
The code you receive will be valid for 30 days, and all you need to do is shoot this off to your new provider, which will be obliged to arrange the switch within one working day. This speedy system ensures there's no overlap, so at no point should you be paying two carriers at the same time. In fact, Ofcom with ban mobile networks from charging any kind of notice period fee after you've decided to switch. This is also where the "cancellation code" comes in, because even if you're not bothered about porting your number, the gaining provider needs this to confirm with your previous provider that the relationship's over.
Though Ofcom now seems to have all the bases covered, it's still putting the proposals up for consultation until the end of June. The regulator intends to have everything finalised by autumn, at which point we'll know what kind of implementation timeline carriers are looking at.