Bad service (and a bit rude)
If I could I would not have made the mistake of giving O2 a second chance and signing with them for 24 months.
Biggest mistake in the past decade I've made.
Bought an iPhone with them that was locked, which makes it useless the 5 months of the year I am out of the country.
Their customer service is quite poor compared to what I've experienced with other companies, and they have a habit of hanging up on people when they don't know how to solve a problem.