se k810 = rm760 (AP)
se k800 = rm590 (AP)

go for 2nd hand SE K850i. 

1.most current hp (mid to high) all hv those mp3 function, bluetoooth n etc
2.u can refer GSMArena, PhoneArena for more info about all phone
for k810 and k800, here GSMarena review
---> GSMArena K800's review
---> K800 vs n73 vs LG kg920
---> k800 vs samsung d900 vs n73

k800 is an older model while k810 is k800 facelifted model.hence, k810 is newer than k800 n hv sleeker look. as for camera wise, both (k800 n k810) are same

here, k810's review

---> K810's GSMarena Review

3. ap diff than the original interms of warranty period and its coverage.thats all.original will give u peace of mind. typical malaysian (like me) will opt to choose ap set one due to cheaper price.hehe.

4. k850 is 5mpx SE, 2nd hand price if u lucky can find under rm800 (can search at garage sales)

why take 2mp camera? with rm900 u can buy sony  k800i,  sony k810 or sony K770. the picture is look so nice for this three hp that have the cybershot technology or take for the latest C series for sony. Xenon flashlight boost the quality of the picture. k800 user here..very satisfied user

Friends, just change the k800i setting to 1mp or VGA when take photo..for me, only resolution increase and file increase, picture quality still same.unless u use the "best pic" mode for k800i. I often use the 1mp setting for k800i. all picture file is around 1xx-200kb only..i think this size very small..and i think almost all the 2.0mp camera is terible due to using the LED light..If u insist to look for the best 2.0mp camera phone, try check got any 2.0mp hp with xenon light. For my knowledge, none 

the only bad thing for the xenon light is that your hp cant use as torchlight ..haiz..and for the difficulties, i think is only the battery problem..most of the SE is power hungry than Nokia..Therefore, make sure ur charger is with u unless all ur friend is using the SE hp too..for the sms, spacing button is different than nokia.and keypad lock is opposite than nokia..that's all.. U will use to it after using 1 week. I like SE because they operate fast and like k800i because it is camera phone and include the top two button shotcut there.Some ppl suggest take k810, but dont have that two shurtcut there..k777 is the latest one, more slim but i not sure it nice or not..andyway, k800i cheapest among all.. I'm looking for second hand k800i now as my spare hp..

since 2006 august until now..depend the usage u use..i turn the brightness to 50%..save a lot of battery..dont play too much songs..

usage for me
less than 10 sms per day, and recieve less than 5 call - 4 days
play songs  - drop very fast..max is 1 1/2 day
heavy sms, call and receive call - max is 1 1/2 day..

i got compare with the n73..both play songs..k800i drop 50% with 70% volume while n73 drop 25% only with max volume..

take photo without xenon flash can take more than 150 picture and above..dont worry
I'm still ok with the battery life..just dont play songs and play games.. this hp no suit for that..

as u can see the light for the xenon is quite strong..if u put the light close to your eye, might nearly blind.
xenon flash should able take more than 50 picture..not too sure
among all the hp, cheapest for having high end camera phone is k800i only..5xx only for ap.why not go ahead and try..I keep find my friend for selling their k800i to me..no ppl want to sell, can u imagine how good is it?

Nokia N73ME?? But a bit old... Personally think that the camera is not bad...