Md. Code, Tax - General § 11–108

The sale or recharge of a prepaid telephone calling arrangement is taxable in the State if:

(1) the sale or recharge takes place at the vendor’s place of business located in the State;

(2) the buyer’s shipping address is in the State; or

(3) there is no item shipped, but the buyer’s billing address or the location associated with the buyer’s mobile telephone number is in the State.