Currently (6/16/2009), the Linksys WRT54GX4 is blacklisted. It corrupts the SIP packets (SIP transformations) and does not allow more than one SIP device to use port 5060 at a time. If more than one device attempt to use port 5060, the device sends response traffic to the device who more recently sent traffic, which is not always the device that originally sent the traffic.
Currently there is no work around and this device cannot support multiple SIP devices using the OnSIP Hosted PBX.
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