I have my 6310i since 2002 and it has NEVER failed me. It is a tri-band device so will work in all parts of the world (this was my main reason for getting one - to use in the USA). Like others have said before me, the battery lasts well over a week and it does everything a phone should do - voice & text. Anything more is just a waste of my money.
Furthermore, it is extremely robust - it takes knocks and drops in its stride. This phone used to be "state of the art" back then, and is still clearly loved by many - as the price on Amazon demonstrates.