Users are reporting that holding it by the bottom left hand corner causes a short between the two built in antennas (one for the mobile phone, one for wireless internet) causing bothing of them to fail.
Apple’s response so far appears to have been “don’t hold it like that. If you must hold it like that, buy one of these lovely cases we’ve designed for it”. (Coincidentally, the first time Apple have ever released a case for their iPhone?)
And people complain about Telefonica.