If an application freezes (it can happen), press and hold the Home button to force quit it.

The iPhone, starting with firmware 1.1.3, features a geopositioning system what works by triangulating on both cell towers and Wi-Fi access points. This produces approximate geographical coordinates that can be shown on a map.

To use this feature launch the Maps application, and tap the icon on the bottom-left corner of the screen.
Note that this features requires you to have an active wi-fi or EDGE connection (this is used to download the coordinates of the cell towers).

Check out this page on Wikipedia for more technical information about GSM localization. 

Connect the iPhone to iTunes, then go the Photos tab, select the option box "Synchronize Photos", and select the folder where your photos are located. Finally synchnorize the iPhone with iTunes by clicking the Apply button at the bottom.

To type an accented letter when writing a SMS (or while writing text in any other application, for that matter) press the un-accented letter and hold down your finger until it shows the accented variations; then drag you finger over the accented letter and release it.

Yes it does.

Go into Settings / General / Info, and there it is. iTunes also shows it to you when you connect the iPhone.

No, it does support only 802.11b and g.

Backing-up all iPhone data (SMS chats, contacts, contacts, calls list etc.) is automatically done by iTunes every time you connect to it. If you later connect to iTunes the iPhone after a total reset, or connect a new iPhone, iTunes asks you if you want to restore it from the previous backup. It is as easy as it sounds.

Attention: the process does not backup settings and data stored by third party applications. Only the built-in apps' data is backed up and restored.