I have iphone 3g 8g , and sometimes when i run some of applications , my iphone escape from applications to the home screen?? is that because i put many applications on my iphone ?? and if it is so , then how many applications i should put ??

When it go from an application to the home screen mean it crash the Application. This may be the cause of : "iPhone is out of memory (RAM), or the application itself have bug ) it's not actually because you install too much application. But if you reduce the number of application your iPhone sure will run faster. From now on if you play a game or open a application that usually crash try to restart your iPhone ( hold down both power and home button until you see a black screen with the Apple logo) . You'll see that game or application will run faster and crash less maybe not at all. Good luck and hope this help.

My friend had the same problem all he did was delete the aps and redownload them through itunes and they worked fine after that

hope this helps

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If you go over the 4-5 pages worth of apps then your iPhone will tend to crash often as the free RAM is being used and there is none available. Try turning your iPhone off after installing an app. Else just remove the ones you don't use.
:D

The phone is starting to crash a fresh restore should do the trick

Probably what it is one of the apps is corrupt and they all need to be removed from the phone, and synced with itunes to put them all back on

That is because applications like safari,mail are always running in the background and when you open more apps the system memory gets low so the iphone quits the app.. Download memtool from cydia. It will help you to close apps running in the background

Sometimes the iphone crashed returning to the home screen much like a computer, maybe delete some applications.

Thats shouldnt matter how much apps you put on ur iphone. this sometimes happeneds when you reactly updated your iphone and you downloaded the apps b4 the upgrade you should try to restore it and this should downgrade your firmware back to normal and everything should be fine if that doesnt work delet the app and download it again hope this helps

The reason why it does that is not because of ur applications and games on the phone, its because after every download or multi downloads of games and apps, u must turn off the iphone and restart it. the iphone also requires the phone is be turned off every day or every other day. the reason for this is because the iphone must be reset other wise its like a normal computer with many many programs open, it chokes. the only way to clear up this used up memory is to turn it off and back on.
a second way that sometimes helps out in different ways is, push the top button and the main home screen button at the same time for 8 seconds.

It may just be that the application in question crashed. You want to remove apps that you don't like or dont use. Keep track of what crashes and when. 
Try rebooting the phone (turn off and back on) if this keeps happening.