so in case u get the phone get the ones manufactured in week 27 or later which can be checked in the battery. if u want a slider in the same range you can always get a n80.
^ In the battery compartment, just under the battery .. there's a sticker with a bunch of barcodes and serial numbers.
Look for a 5 character string with the format xxWxx (eg: "04W51") - this is the manufacturing date. The first two characters in the string refer to the year (04 = year 2004), and the last two characters refer to the week (51 = week 51).
So what you should look for is any phone with a manufacturing date from or greater than "07W27".