Be careful with the overseas ones - a number of the cheaply available ones are ones that were sold through a specific VoIP provider, with their firmware from the factory. They have generally then had firmware cloned across from another device, and people have run in to all sorts of dramas with MAC address conflicts etc.
In the VoIP world, it's often a matter of getting what you pay for, both in terms of hardware, and service providers. As you've already seen, there can be huge problems getting things going, and paying that little bit extra can save you a lot of frustration in terms of use.
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