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I don't mean people sharing one channel Phil, but the person at the other end.
In full duplex you can talk and the person on the phone to you can as well and it's like a face to face conversation. Just like a normal phone. But the cordless home speakerphones use the old simplex method that only allows one person to talk at either end. If you are talking and the person at the other end interrupts they won't hear you at all, they'll just get a moment of silence while they are speaking. It can only send or receive, not both.
rojash, I've seen them selling plenty of unlocked mobiles at the Carphone Warehouse and they weren't a lot dearer than the dedicated ones. And the cordless phones I've had to suffer from my end have been top of the range at over �100 and still unable to go duplex. I suppose it's just a way of maximising profits really but they're still insisting on using outdated and inadequate technology. Sad really.