A service control point transmits a recharge request message or advice of charge
to a mobile client resident in a wireless communications device. The message is
first received by a wireless telephony application server that then forwards the
message to a wireless access protocol gateway. The wireless access protocol gateway
then sends the request to the mobile client. The user of the mobile client responds
with an affirmative or negative answer to the request to recharge the prepaid telephone
airtime account. The service control point then either recharges the account as
instructed or lets the account expire, depending on the response from the user.