No, only on the purchase. Taxes on the phone bill are based on the billing address.

That depends. You will need to see how IL allows you to be taxed on your cell phone bill. There are 3 possible ways.

1. Billing address determines tax. In this case, you will have the highest tax on your bill since Cook County recently raised their sales tax to 10.25%.

2. Tax based on where phone was purchased. This would lower your taxes compared to Cook County.

3. Tax based on your phone number. As long as your area code and exchange are outside of Cook County, you could be taxed at the rate where the phone number is registered.

I don’t know the specifics of IL sales tax law to give you a better answer.