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We are a cox telephone customer and wondering what bluetooth headset would handle 3 phone lines.
I think you mean 1 Bluetooth headset with 3 simultaneous connections. Multipoint allows 2 simultaneous connections. There is now an Advanced Multipoint but I don't believe if it allows more than 2 connections.
I don't think you're talking about pairing because multiple devices can already be paired to one headset...just not simultaneously used. Multiple devices in this case would mean: to be remembered, woken up and quickly swapped out to use.
I'd search Bluetooth Headset 3 Simultaneous (or Concurrent) Devices.