
Not to spoil the punch line, but the phone can be paired to a mobile phone via Bluetooth, making it effectively a great handset for his iPhone. So it’s genuinely useful even without having a SIP line registered.
Other companies like Mocet & Invoxia (review) offer similar capability in dedicated function devices, but these cost considerably more than the GXP-2160, which is currently listed on Amazon for just $99.
I wish I could do the same with my Polycom VVX-600!