BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a communication system of an exemplary embodiment of the present invention;
FIG. 2 is a schematic diagram of a communication system of another exemplary embodiment of the present invention;
FIG. 3 is a schematic diagram of functional modules of a voice over Internet protocol (VoIP) modem of an exemplary embodiment of the present invention;
FIG. 4 is a schematic diagram of functional modules of a VoIP modem of another exemplary embodiment of the present invention;
FIG. 5 is a flowchart of a method for detecting VoIP service of a further exemplary embodiment of the present invention;
FIG. 6 is a flowchart of a method for detecting VoIP service of a still further exemplary embodiment of the present invention; and
FIG. 7 is a flowchart of a method for determining whether a gateway is reachable of FIG. 6.