If you need to find your iPhone serial number, International Mobile Equipment Identity (IMEI) number, identifier, or ICCID number this article shows you several different ways you can locate it.

Pictures and screenshots taken with the iPhone are stored on the Camera Roll. When you sync or perform a restore, iTunes creates a backup the contents of your iPhone, including the Camera Roll. The more pictures or other multimedia files that are on the Camera Roll, the longer a backup or restore will take.
Improve backup and restore times by regularly importing the contents of your Camera Roll, and then sync that content back to the iPhone.

iPhone OS 3.1 or later offers the ability to view tethering data usage in Settings > General > Usage.

Applications on iPhone or iPod touch may close unexpectedly because the device has begun to run low on application memory. This does not mean there is too much data stored on the device, but simply means that it is running too many memory-intensive tasks.
Some examples of this issue:

If you have many Safari web pages open on your iPhone or iPod touch, Safari may close and the iPhone or iPod touch will go back to the Home screen (where it shows all the application icons).
When listening to music or podcasts, watch video, etc. playback may stop and the device may return to the Home screen.
While using Safari or Maps and listening to music or podcasts, iPod audio playback may stop.
Applications purchased from the App Store quit immediately after you tap them.

Your iPhone or iPod touch may experience one of the following symptoms:

Multi-Touch display (or touchscreen) does not respond
Portions of the Multi-Touch display do not respond
Multi-Touch display is very slow to respond