Three has started to upgrade its customers to 4G free of charge. Starting this week, some customers with compatible handsets will find that they can receive 4G data speeds in London, Birmingham and Manchester.

Not all customers will be upgraded this month though, as the rollout could take a few months, with Three promising to upgrade all customers by the end of Q1 2014 - the end of March, basically.

By then, more locations in the UK will be able to receive 4G signals. Reading will be added this month, while 50 other cities are due to be switched on in 2014. This includes Aberdeen, Bolton, Cardiff, Coventry, Brighton, Edinburgh, Liverpool and Newcastle. Visit for a full list.

Three also announced that it has lifted data roaming charges for the US, allowing customers to use their existing minutes, texts and data allowances when travelling in the country no matter which foreign network they are connected to.

READ: Three now allows you to use your own data plan while roaming the USA, no more ridiculous costs