A signal booster for my old phone

I already got myself an iPhone but I am not giving up with my old Nokia phone. I just love it's QWERTY pad and I think I got so used to it already. Its what I use for calling and sending messages as well. But lately I noticed that it's signal is dropping, or sometimes my call will be cut as soon as the receiver picks up the other line. Im thinking of trying out the phone booster , as suggested by one of my friends. Hopefully it will do the trick, or else I will be forced to get myself a new phone, or might as well use the iPhone for sending messages and calling. Do you have other suggestions for new phone units? Or do you have other solution to my phone's problem?