That's a good point. The flight I wanted was going within a couple of minutes of midnight GMT for the days prior to when my flight became available. I discovered that the Exec Club USA number stops at exactly midnight GMT. On the night my flight became available (I'm in the UK so it was 1am my time) I rang the USA BA customer services number getting through at 11.57. After going through all the security measures and saying what I wanted to do it was 11.59 and 45 seconds at which point I was told that they couldn't turn the single into a return on that number as it was too complicated for their computer system and I needed to call the Exec Club number which was closing in 15 seconds! The only alternative would have been to call the Australian Exec Club which was open at the time but I gave up and went to bed. As luck would have it two Club seats were still available the next morning and I called the UK BA Exec Club number when it opened. They booked the seats, charged me the correct return price rather than the two singles price which would have been a lot more and there was no charge for calling as you can't do it online.

Doing this again, I would either call Australia BA Exec Club as it's cheap via Skype or maybe try the US Exec Club but call a little earlier as I guess if you get through just before midnight they will complete the call.