I am in the process of moving to 3 due to awful 4G speeds on O2 in my area. My concern is that I could potentially incur an early termination fee of nearly £300, but I can't justify paying that because frequently I couldn't use the 4G service (slow speeds/non-existent connectivity even with good phone signal), which meant it was not just having a major impact on my personal life but also my ability to run my own business. I have acquired a PAC code, but my number has not been moved over to 3 yet. I have tried to raise a special case with O2, but most people I have talked to have emphasised that I will need to pay the fee, only 1 person said they could waver it. If I do have to pay it, then I will have to move back to yourselves, but then I will not be able to use the 4G service that I have paid £25/month for, which I think isn't acceptable.
I would be interested to know where to go from here.
Officially, you need to follow the complaints process and see if they will give you written confirmation to leave without penalty.
They may do if you have a refresh contract and return the phone https://www.o2.co.uk/how-to-complain