T-Mobile has launched an investigation into the computer failure that brought mobile telephone services, including SMS messaging, to a halt for about three hours on Tuesday.

A company spokeswoman, Marion Kessing, said sabotage was highly unlikely as a cause.

The Bonn-based offshoot of the giant German telecoms group Deutsche Telekom is also attempting to assess how many of its 39.1 million German mobile phone customers were hit by the outage.

However, a T-Mobile spokesman told German press agency dpa on Wednesday that the company was not liable to pay compensation as a result of the breakdown in its network.

But in a gesture of contrition, the company said customers would be allowed to send text messages for free all day this Sunday within Germany.