It didn't even occur to me to wonder whether mobile phones would work in a field in rural Somerset...

IIRC the Glasto site itself has reasonable coverage; it's quite open, and a broad shallow valley rather than lots of very narrow and deep ones. Mother Nature still gets her way in that part fo the world when she really wants it - when I go riding near Minehead the escorts quite often find they have no signal when we're down in the woods but it opens up again on the moor tops.

Shame you didn't make it to the circus field though - that's an absolutely fantastic bit of the festival, jam-packed with colour and life, it really epitomises the atmosphere as far as I'm concerned :)