What?! Did I read it wrong? Today, even a teenager at secondary school has a mobile phone, but you've just planned to buy one.
However, if you have never used a mobile phone before, there are at least two types of mobile you can consider. First, just a phone: a Nokia 1202-2, a phone with mono chrome display. If there is anything special with the Nokia 1202-2, then it is a flashlight. Though it doesn't has any special function than just a phone, it is very good in quality. Never error, never crash, never worry about virus. If you accidentally drop it, don't worry, just pick it up. It will still work fine. Cost? I bought one @ US$30. Not sure what's the price at your place.
Second, a phone with everything on it. Wow, there are too much choice, and I really can't suggest one. Maybe you should try reading the "Computer Talk" thread, Crobato has posted a lot of news about new mobile phones there such as the HTC that use Windows Mobile for its operating system. It's a phone that has many functions. Since it uses Microsoft's Windows Mobile as its OS, it of course has Word and Excel. However, the more functions, the more chance of getting error and it might cost you from the range of US$500 ~ US$800.