If you want to switch networks, you may have to unlock your mobile phone. But this can be surprisingly complicated and expensive, as Sue Hayward found.
Considering mobile phone companies are in the business of communication, you'd think they would be pretty good at it.
But when it comes answering a simple question such as "how do I unlock my phone?", it can be hard to get a straight answer.
When you buy a mobile phone, it's usually locked to a particular phone network.
Getting a mobile phone unlocked
So, if you want to take advantage of deals and promotions from other operators, you need to unlock it.
My daughter had a mobile phone on a Vodafone pay-as-you-go (PAYG) deal.
After a year wanted to switch networks to take advantage of a £1-a-month contract deal with another provider.
When I rang Vodafone it all sounded very easy and fee-free.
But further along the call centre chain I was told this would incur a £19.99 charge - a big fee considering you can get phones unlocked at high street outlets from around £5.
Fee-free mobile phone unlocking
I rang Vodafone's disconnections department to check this charge was correct.
They insisted it was, although they did offer to waive it as a gesture of goodwill.
I agreed and was passed - yet again - to another person who then told me there was actually no charge at all to unlock a pay-as-you-go mobile phone once it's over a year old.
So, had I not questioned the charge, Vodafone would have been £20 richer at my expense.
However, despite being promised the fee-free unlock code within three to five days, I was still waiting three weeks later.
Are mobile phone networks playing silly games?
Call me cynical, but what's to stop mobile companies deliberately playing silly games when it comes to providing unlock codes as, naturally, they don't want you to switch?
Well, communications industry regulator Ofcom says there are no rules to prevent mobile phone operators locking phones to their networks.
And any unlocking charge imposed is pretty much down to individual operators, providing it's written into their terms and conditions.
As you might expect, charges vary depending on which network you're with.
Mobile phone unlocking cost by network
O2 charges PAYG customers £15 a time, but this option is only available after a year.
Orange charges £20.42 for both PAYG and contract customers and with T-Mobile the charge for unlocking a handset is £15.32.
With both these mobile phone networks you can ask to unlock your phone after three months, although if you're on a contact you will need to cover the cost of any remaining term.
Vodafone confirmed the £20 charge for PAYG phones but say this is paid regardless of how long you've had the phone.
This conflicts with the "free after a year" information given to me by Vodafone's call centre staff.
What do you need to get a phone unlocked?
Along with the make and model of your handset, the key bit of information you need is your phone's International Mobile Equipment Identity (IMEI) number.
This is a unique serial number which you can find on the original box or by dialling *#06# on your handset.
How long should it take to get a mobile unlocked?
The time taken to hand over the unlock code depends on the network operator.
O2 says it's up to 10 days while both Orange and T-Mobile say it should take up to 30 days.
In some cases can take up to three months, depending on your handset.
And Vodafone says it can usually provide the unlock code within 72 hours, although if it has to request one from the manufacturer it can be up to ten days.