If the source of the internet is your home router, then any online activity you do will count towards your monthly limit (although some ISPs don't include upload bandwith in the limit).
If the source of your internet is the local WiFi hotspot (like in Westfield shopping center for me), then no, it won't count towards your monthly limit.
If the source of the internet is 3G (e.g. WiFi hotspot through an Android smartphone), then it will only count towards the limit for the 3G service (in my example, it'd be my limit with T-Mobile).