Confirm that local network access does not incur ISP costs

I would like to make sure that when I connect my mac and phone using airdroid locally (192.168.xxx.xx) to my home network I do not incur ISP costs.
The Setup:
Billion 3G wireless router
3G data card on contract
Samsung gallaxy s2
Macbook Pro

I connect phone to mac using the local routers wireless password I set up from the router.