These messages have apparently been broadcast from a Lockheed Martin EC-130 aircraft known as Commander Solo overflying the region and are using the frequencies which belong to the 'Great Man Made River Authority' (GMMRA) which is Libya's authority responsible for artificially transporting water from wells in the Sahara desert via a big pipe to population centres in the North. Why NATO would have chosen these frequencies is not known, however there is (or was) apparently an ALE network on these channels that was presumably in regular use and hence there would be several receivers across the country in 'important offices' which would hear the PsyOps transmissions.
Frequencies reported in use by the GMMRA in recent times include 4200, 5037, 5047, 5300, 5368, 5768, 6884, 7000, 8161, 8200, 8800, 9218, 9250, 9375, 10125, 10375, 10404 and 11100 kHz. Previous reported frequencies also include 3000, 3900, 4050, 6800, 7805, 7900, 10215 and 10250 kHz (thanks to Btown Monitoring Post).
Of the above, NATO PsyOps transmissions have so far been heard on: 6877, 9376, 10125, 10404 kHz. Note that the 10125 kHz frequency is slap bang in the middle of the 30 metre amateur band but as this is a shared frequency with other services the transmission by the military does not contravene the ITU frequency allocation tables and is therefore, effectively legal. The use of 7000 kHz by the GMMRA is not, however, legal as this is an exclusive amateur allocation. Initially, many of the PsyOps transmissions were jammed (presumably by the Gadaffi regime) however they no longer appear to be so.
Here's the Wireless Waffle recording of Commander Solo on 10404 kHz made at 14:00 GMT on 12 July 2011. The transmission ceased at 14:20 GMT. The noise underneath the transmission also ceased around the same time, however whether the two are connected (ie the noise is an attempt at jamming) can not be confirmed. Given that this recording was made in the UK, it is clear that the power of the transmitter used by Commander Solo and his ilk must be reasonbly high. Judging by the signal strength and general propagation conditions at the time of the recording, a radiated power of at least 1 kiloWatt would seem about right. As normal HF aircraft radios have powers of at least 200 Watts, this seems quite feasible.
Of course, all that the Colonel has to do to stop the NATO transmissions becoming a nuisance, is hand out free power line adaptors to at least one house on every street and all short-wave frequencies would be instantly jammed. Perhaps Colonel Gadaffi is an investor the Comtrend PLT devices that do all the damage and the reluctance of Ofcom to do anything about them is part of some previous UK-Libya trade agreement on arms sales. Surely now that the UK is part of a force against Gadaffi, Ofcom can now breach the terms of this agreement with the Libyan government to pollute short-wave and finally get rid of the menace of PLT?