A quick look on ebay, the K800 has been selling for £20 or so which is surprising. So possibly are worth selling.
On ebay you can show only sold items in the search, which gives you a good idea of what an item will sell for.
had p910 back in the day.Are any of those phones P-series? E.g. P910 or P990? "P" stood for PDA phones which is what we call smartphones nowadays. They had touchscreen, full internet access and the ability to install apps via Java and also from the Orange store. Back in 2005They could fetch a bit now.