If you are going to buy a new Sony Ericsson K750i or maybe just taking it back from the service center, you might want to test the handset to check if everything is working fine. The simplest and the most comprehensive way to do this is using the Service Menu.
From the main screen –
Move the joystick right once then press *
Move the joystick left twice then press *
Move the joystick left once and then press *
You will see the Service screen with three options. Select the Service Tests option. A list of tests will come up to check all the functions of your phone. Go through all the tests and accept delivery only if satisfied with all the results. Of course, this doesn’t guarantees against any future defects but at least you can be sure that you accepted a fully working device.