Most cellular modem providers do have a monthly data cap. Cricket is one of the few that does not. However, if you go over a certain amount of bandwidth in a particular month they may lower your bandwidth to a slower speed.

There are a number of reasons that one may want to limit bandwidth on a Cisco router. If one is using too much bandwidth, that could slow the download speeds of other users in the area. Also, some internet services cap the amount of bandwidth allowed.

When making a VoIP call from your phone you will be more than likely accessing bandwidth from your carrier. If you are charged for your bandwidth usage or go over your bandwidth cap, you essentially will be paying fro the time you spend on your VoIP calls. Basically, yes.

Bandwidth is used whenever you are on the internet, so unless it is offline there are no virtual worlds that use no bandwidth. However, most Internet Service Providers have very high bandwidth caps, usually about 250 GB (which is equal to downloading 250 movies) or no cap at all, so you don't need to worry about bandwidth so much.

Usually a maximum amount of bandwidth, that you are allowed to send either in megabits per second or megabytes transfered.