Use the table below to help you decide which network is best for your needs.The next step is to check that you’re not still under contract and are free to switch. Once you’ve established that you are, sign up for for the SIM only deal you've chosen. In the meantime, ring or email your network to tell them you’d like to leave.
Here, you'll find a month-by-month breakdown of exactly how much data you've been using.
If you're out of contract and happy with the phone you've got and don't want to upgrade to a newer model, it's smart to switch to a SIM only deal.
Otherwise, your network will continue to charge you the same monthly premium as when you were still paying for your handset.
So if you want to use another network's SIM, you'll first need to unlock your handset.
Conversely, when it comes to O2 phones sold on pay monthly plans, only some are unlocked.