The phone just rang and it displayed "unavailable" instead of a number. When I answered, it was a voice I didn't recognise so asked who was calling. Here's the strange part - the guy said that I called him. Turns out his phone rang at the same time as ours.

Does anyone know what could have happened here? It's not all that important - I'm just curious.

Some "wind-up" piece for a radio show maybe?

Calls from abroad usually say 'Unavailable'.

Or it could be Three way calling, were some calls them and then quietly puts them on hold, calls dials your number and connected the two calls together and makes it look like you've called each other.

Or it could be just a fault in the area.

Were you on the phone just before it rang?

Perhaps someone tried to call you and got engaged tone, so used call back.

Calls from abroad usually say International, not unavailable.

Great thing about switching to VoIP is I get to see all international numbers on the CLID device.

I didn't know the person (ruling out callback) and they were in this country (at least I assume they were), so I think the most logical explanation is a fault at the exchange (or the windup as DonnyDave suggested! Even if it was, I never said anything daft ).

Well when I had a BT caller display unit on a Telewest line it said 'Unavailable' when people called from abroad or from certain UK networks. When you dial 1471 from a Telewest phone it will say something like 'Sorry the last call was from a network that it is unable to transmit numbers'

On a mobile, the international number shows up if its from a mobile, so if its from Germany it starts of something like +49.

One thing with Number display and 1471 on Telewest, the services don't tell you if the person who called was using a payphone. So when I try to return the call, it just rings and rings until someone answers and you hear the two beeps.

True cable CLID is a bit hit and miss, I think they do only use unavailable when from a abroad, BT will flag international. Just a shame Telewest can never do anything properly, yes they were the first in the UK to give the time and date with the number on 1471 when BT were only giving the number, they have good ideas Telewest but poorly implement them.

Anyway none of that is a problem for me VoIP has none of this hiding International numbers, it just displays them.

As the OP was on BT they will get International flagged up on international calls, and unavailable on calls from within the UK that can't/don't transmit numbers.

I thought you might say that - I should have explained.

This has happened many times to me (usually at work, but not always). What happens is that the person who calls you leaves a callback request. By the time that callback occurs, the initiator has moved (e.g. end of shift, gone to meeting, etc) and someone else is sat at that desk, hence 2 people with nothing to say to each other are connected.

Sometimes also occurs where the initiator 'borrows' a phone (e.g. visiting someone) but has now left or where one phone number is shared by others (again usually at work).

I had the same thing happen to myself on Saturday, was watching the Scotland game in the morning, and the phone rang, the missus answered it, and after hearing her shout hello down the phone, i thought it was yet another of these wonderful cold calls, turns out to be someone on the other end of the phone who says that we called him, the guy said he too was watching the football and his phone rang, saying that we phoned him!