A method for using an account balance to limit application of cellular-PBX integration service. A cellular wireless communication device (WCD) will be allotted a quantity of cellular-PBX integration service, such as a number of minutes of use per month for instance. The quantity will be decremented a the WCD uses the service, and the WCD may be precluded from benefiting from the cellular-PBX integration service upon exhaustion of the balance. In one embodiment, for instance, when a radio access network (RAN) that serves the WCD receives a call request for the WCD, the account balance can be used as a basis to decide whether to pass the call to an IP PBX server that serves the WCD or whether to have the RAN handle the call.