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If you can register your devices one by one, but not all of them individually, typically this is a Router problem.

Many inexpensive or low end routers are not designed for multiple SIP devices behind NAT. These routers are unable to keep the ports tied to the IP addresses or keep open the pinholes that make NAT work. These routers are typically available a electronics and office supplies stores and usually under $150.00.

If you have an option called "SIP ALG" and it is turned on. Try turning this off and restarting the router. This has been known to cause many problem.

If you have the capability to take the same phones to another location with a different router, this is a good test. If it works fine you know it is the Router.

If you are still having trouble, please contact Talking Platforms support for a reccomended list of Routers.