Monthly cost per child: £35

Among the biggest expenses for parents of teenagers - they want the latest phone and the freedom to use it. There are two options - a contract or pay-as-you-go.

Cost-cutting tips: It may seem a daunting task but rather than just opting for pay-as-you-go - where calls and texts can work out more expensive - check out all the price plans available and find one that will be the most cost-effective for your teenager. Look for plans with a good text package - bearing in mind that this is the way teenagers communicate.

Be firm and set a fixed amount. Tell your children that they have to learn to use the phone wisely. Don't give in and top them up when their credit runs out - it will help to teach them that there is not an endless supply of cash.