Your iPhone basically is a Unix (MacOSX) power-based phone, that sounds cool!?
So to speed up your iPhone, you just simply stop un-used, or rarely use services (call daemon in Unix)
Here are 4 steps:
1/ Get access to your iPhone terminal (ssh, MobileTerminal)
2/ Learn launchctl command (with parameter: start, stop, list, load, unload)
3/ Using launchctl with parameter "list" to see un-used, rarely used daemons, and "stop" it, or "unload" it from startup
4/ Move (do not delete - in case you want to get back those services) those .plist file away from /System/Library/LaunchDaemons/
These are links for your reference:
1/ Related to command line: http://www.ifans.com/forums/threads/ssh-daemon-wont-start.87039/
This shows you how to load, unload daemon from startup also
2/ Related to daemons: http://www.ijailbreak.com/how-to/how-to-remove-launch-daemons-to-increase-speed-battery-life-disk-space-part-two/
3/ This week, when I reviewed my post, and after working around I found this very detail and interesting article. It explains very detail which Daemon you can stop & in which situation
http://forums.macrumors.com/showthread.php?t=1371126
Finally, use it at your own risk, but warranty there is no damage to you iPhone, iPad
