To get Cydia on you iPhone, the phone will need to be jailbroken. It depends on what generation iPhone you have and the firmware installed.
Every iPhone on 4.1 can be jailbroken using pwnage tool, redsn0w, greenpois0n, or limera1n.
I personally have an iPhone 3GS with 4.1 jailbroken with limera1n.
Cheers
Simply update ios
go to cydia, manage, packages, bitesms, modify, then remove
Jailbreak your iPhone
you go on a website called jailbreakmatrix
No
Yes but your iphone has to be jailbroken and have Cydia.
I believe it is the same thing.
click on Restore in Itunes
Don't download loads of apps. Cydia alone will most likely not crash your iPhone, but installing many apps increase chances.
Yes, if you restore your iPod or iPhone on iTunes it will delete Cydia. The restore function on iTunes restores your iPod or iPhone to its previous settings.
No. These are apps that you get when you jailbreak the iPhone.
There is no way to do that. If you jailbreak your iPhone there is an app on Cydia that does that.