actually i had the same problems, but i did managed to solve it, this is my solving method step by step below,
1, cleanup all the unread sms, dont leave it till like 100 over like i used to, it will lag everytime when u trying to text.
2, restoring to the iphone using itune( remember to back it up all the apps and photos, cos if later when restroing using the icloud , the most time consuming part its the apps installing and photos from wifi) so just choose restoring from icloud, its only takes like 10minites for the phone to get all settings like wallpaper, phone setting ,contactes, etc but not the apps , ringtones and photos. later u could sync all the rest with itune, its faster this way.
3, uncheck calander and also some apps u dont really needed in noticifation.
4, dont over keep to much photos and videos on the phone, back it all up on PC time to time.
5, dont ever jailbreak your iphone after ios 5.1, its useless for being pretty if super lag, there tons of free apps on itune.
6.quit some background apps time to time.
7, restart ur iphone time to time like once every month. ( holding home and the top left botton)
8, wish u luck buddies X3..