NTT DoCoMo may already have 56 per cent of the mobile phone market in Japan. But that hasn't stopped it innovating through handsets such as Mitsubishi 's D702iF, a new handset that tracks the fertility of female users each month in a bid to help them conceive.

The phone, which has been seen before in prototype form and went on sale in Japan this week, takes user-inputted menstruation data and works out when attempts to conceive are most likely to succeed, then prompts the user to make 'appropriate' plans.

Other features include 'camouflage melody', a simulated incoming ringtone to be used as an excuse to escape unwanted attention in bars and the like. The D702iF sells for ¥6,000 (£27) with a new DoCoMo contract.