Make sure you have a strong enough signal – the display shows you how strong the signal is. If it isn't strong enough, try moving to an open space or, if indoors, move near to a window.
If you can't receive calls, check that the ringer volume is not too low or switched off. Also, check that your calls are not diverted to a different phone or to voicemail.
If you've not used your phone before, it may be because it is not activated: to activate your phone, please contact us.