The consumer group Which? is calling on mobile providers to automatically unlock phones at the end of contracts and to sell them unlocked to pay-as-you-go users.
Locked phones are restricted to a single network and Which? says this discourages users from switching providers and finding a better deal. Customers can pay to have handsets unlocked, allowing them to use a sim card from another network – but rules and charges vary between providers.
Which? found that Virgin charged £15.32 to unlock a handset and Tesco £20 within the first 12 months of a contract. While O2 charged £15 for pay-as-you-go users, those on a contract could have their handset unlocked at any time without charge. GiffGaff and Three provide all devices unlocked.
The Unlock Better Mobile Deals campaign also accuses providers of not putting consumers on the best tariff.
Which? executive director Richard Lloyd said: "Mobile phones are an essential part of daily life for many people and consumers shouldn't be locked into contracts that do not suit their usage. We want to send a message to mobile phone companies that they should help customers get a better deal by alerting people that their contracts are about to end and by unlocking handsets for free."