Yes, much to the dismay of your ISP, an Android device can be used for "Tethering" or as a mobile WiFi hotspot. Simply go Settings->Wireless & network settings -> Tethering & portable hotspot.
EDIT: This only applies to Android 2.2 and above.
You can use a wireless connection if you have a wireless router
a wireless modem means it has a wireless router built in. A wireless router means just a wireless router. if your modem is not wireless, you will need just a wireless router
It does not matter if you are connected through wireless or cable, your router can provide firewall protection for all of its ports on the LAN side. If your question is: Is my wireless router's firewall protecting me, although I do use it for wireless connectivity, the answer is yes. Your routers firewall protects you whether you use the wireless option or not.
Your router WILL need to be wireless to connect wirelessly to your Xbox, but you can use an ethernet cable if your router is not wireless, straight from the router to the XBOX
You can use router of G or N type and the same type wireless adapter. Of course you can use wireless N adapter with G-type router and reverse.
yes
802.11
Yes.
wireless modem is called that because it has a wirelss router built in. wireless router just a wireless router. if your cable is not wireless you can buy a wireless router or a cable modem with wireless router
there has been a misunderstanding between modem and router. some people use only a modem to connect wirelessly and some use a modem and a router. The fact is there are two types. first type is a modem with built in router, second is router itself. this will clear your mind. you don't have to buy a router to go online, just a get modem with router built in
You can't add wireless router to your computer. You can a wireless router to your network. If you do so, it does make your network wireless. In order to use your network wirelessly you need to have wireless adapter for all your computers you want to be connected wireless.
No. You can not attach a router and use a standard Verizon Wireless aircard as a wireless access point. This is why they have MiFi which is essentially a wireless access point.