I am certain that it has nothing to do with mobile phones, although I too thought that my phone was ringing on vibrate when I noticed it. Mine is in the left outer thigh, about midway between the knee and hip, coincidentally where the phone would normally sit when deep in the left pocket.
However, I only started noticing the vibration after recovering from having both ACLs reconstructed after a motorcycle accident (knee reconstructions). It was not long after having the operation that I reported vibrations or twitching in that location to the surgeon, but he thought nothing of it.
Leg strengthening exercises seem to get rid of if, but it appears that any muscle wastage brings the sensation back on. I've been getting it a bit lately since sitting around at work being lazy. I am now certain that it is blood flow related, as I can pinpoint the location and it is in time with my pulse. It isn't a thump, thump, thump like a normal pulse, but a vibrating sequence. In fact after giving it a good rub, it's stopped doing it now.
Don't just blame the mobile, consider muscle tone first. I'll now carry my mobile in a different location and see how that goes. But as long as my foot isn't blue and there's no pain, I'm not overly concerned.
Hollywoodbigshot