It depends on the country you purchased your phone from but generally the answer is YES.
Unlocking a phone to allow its use on a different network or carrier is legal.
For the majority of people who see this article, you will want to know that phone unlocking in the UK is entirely legal, with no limitations at all. This has been confirmed to us by the Metropolitan Police, who we contacted after they removed a previous article we used to link to. For official confirmation, please read the excerpt below, taken from the Mobile Phone Crime Unit:
A 'locked' phone is one that at the point of manufacture has been tied to work on a single network as a commercial condition of use. That restriction can be lawfully removed as it is merely allowing the consumer to have a choice of provider. 'Unlocking' is regularly seen advertised in high street stores and is not illegal.
In the US the situation has changed recently, only allowing those who purchased their handsets before Jan 29th 2013 to be able to unlock theirs legally. However, this is currently under review after a phone unlocking petition was submitted to the White House and a Congressman's response read that phone unlocking “should be legal”. With over 100,000 signing this petition and the response it has received, we expect this law to change.
In most other countries, including Ireland, France, Germany, Italy and Spain, phone unlocking is also entirely legal. However, for more information please visit the SIM Lock page on Wikipedia that details the laws from a large list of countries in regards to phone unlocking.
Will the law change as it did in the US?
At the minute, no - there are no plans to make phone unlocking illegal anywhere else around the world, especially considering the negative impact it has had in the US market. In an attempt to justify this, we got in touch with a leading UK phone network and asked for their thoughts. In response to our question "do you think phone unlocking will remain legal?" Three UK were able to respond with "no reason why not".