How to... upgrade to a new mobile

Sim-free: Paying the full price for a phone without a contract is expensive - the Nokia N97 costs £449

Sim-free: Paying the full price for a phone without a contract is expensive - the Nokia N97 costs £449

If Santa brought you a mobile phone in 2008 and it was on a contract, then it may be up for renewal now, and you may be entitled to a cheap or free new handset.

If your contract hasn't expired, you can still buy a new handset and put your sim card in it. But this means paying the full price for a phone without a contract (called buying sim-free). This is expensive - the recent Nokia N97 smartphone costs £449 from 

Or you could buy a phone on a pay-as-you-go tariff and put your sim in that. This is a bit cheaper but check it will work with your sim card - nearly all pay-as-you-go handsets are locked to a particular network.

If you're entitled to a new handset, you're in a strong position. Networks offer existing customers a new phone cheaply or even free - the cost is subsidised as you're committing to a another contract period of line rental and call charges. But many new contracts are for 18 months or more.

Check recent bills to get an idea of how many minutes of talktime and how many texts you use each month, and decide if you should change your tariff - a pricier rental may be better value if you regularly go over your bundled minutes.

And consider switching networks. you can take your number with you by asking for a PAC code (Port Authorisation Code) from your current network - at which point they may offer you a better deal to stay put. you can upgrade at an independent retailer:

Carphone Warehouse can guide you to the right network and identify the best deal for you. if you're looking for a decent basic phone, try the Nokia 6700; for email, it's hard to beat the BlackBerry Curve, and if you want a sophisticated touch-screen smartphone, the Palm Pre, Nokia X6 and the desirable Apple iPhone are the stand-out handsets.

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