A method may comprise downloading a message client on a first mobile wireless device and authenticating, via the message client and the first mobile wireless device, a first mobile phone number of the first mobile wireless device to a service for transmitting and receiving packet switched messages. The authenticating may be performed via an SMS protocol. The method may further comprise transmitting, after the authenticating, a request including at least information corresponding to a second mobile phone number of a second mobile wireless device, to determine whether the second mobile wireless device corresponds to a subscriber of the service. A response to the request may be received indicating that the second mobile wireless device corresponds to a subscriber of the service. A message format of the service may not be an SMS message format, a MMS message format or an EMS message format.