A user activity, which may be a debit or credit card transaction or an online access, is approved, or proximity between two users is confirmed, based on a response or other acknowledgement from a mobile subscriber terminal. The mobile subscriber terminal acknowledgement is generated in response to a query from an authorizing entity associated with the debit or credit card, or another mobile subscriber terminal, and indicates whether or not the mobile subscriber terminal is within a maximum allowable radius from a specific location included in the query. It is noted that no specific location information is included in the mobile subscriber terminal acknowledgement. An application downloaded to the mobile subscriber terminal may generate the above-described acknowledgement.