I switched to Three after years on O2 (since the Ericsson mobile phone with the solid antenna and fetching brown front face and original Snake built in) since despite O2's continued promises they never installed anything better than GPRS where I live. Eventually I decided not to be a mug any more and checked coverage with other carriers and Three had a decent SIM only plan and also had 3G coverage at my house and 4G where I work so it was a no brainer.
O2 tried to "tempt" me to stay with them when I phoned them for the transfer code so I could keep my number. I told them unless they had a 3G mast on a truck to where I live as we spoke then there wasn't a thing they could say that would keep me with them.
Other than a couple of shady things that Three have done (like not being able to cancel data bolt on things via the web but being able to easily sign up for them, you have to phone to cancel and good luck getting through during times you have free to phone up) I haven't had any problems - I get decent 3G/4G wherever I happen to go now and I pay less than what I was paying O2.
O2 tried to "tempt" me to stay with them when I phoned them for the transfer code so I could keep my number. I told them unless they had a 3G mast on a truck to where I live as we spoke then there wasn't a thing they could say that would keep me with them.
Other than a couple of shady things that Three have done (like not being able to cancel data bolt on things via the web but being able to easily sign up for them, you have to phone to cancel and good luck getting through during times you have free to phone up) I haven't had any problems - I get decent 3G/4G wherever I happen to go now and I pay less than what I was paying O2.