Pilots are taking place in Easingwold, in North Yorkshire, Leiston, in Suffolk, and Glasgow city centre. They will evaluate how the public reacts to the alerts.
The government expects as many as 50,000 people will receive the texts this autumn. They will be marked as test.
A similar system is already in use in the US, Netherlands and Australia.
Read more: Latest 4G news, reviews, videos and specs
Those systems are used to warn the public about hazards such as fires and industrial accidents. They are also used in the US as part of its Amber Alert anti-abduction system.
The trials were announced by the Cabinet Office. It is working with O2, Vodafone and EE to conduct the experiment.
According to the BBC, the tests will begin later this month and continue throughout October and November. Cabinet Office minister said that it would only be used in a “genuine emergency”.
Read more: Best smartphones to buy in 2013
Examples include severe weather, pandemics and attacks on critical infrastructure.
Those who receive the texts will be asked to provide feedback. They will also be invited to attend local focus groups to improve the system.
The system is a response to criticism from the Strategic Defence and Security Review conducted in 2010. It said that the government needed a more effective system to warn the public in emergencies.