One way to look at magic – if you want to try and make it logical or follow the currently understood laws of physics and nature – is that it may affect the natural tendency of things to break down, go wrong or wear out. So, when Harry, or a mage is near a light bulb, which radically increases its chances of burring out right then. And the more infused with magic (not necessarily obviously more powerful), the greater that tendency is.
Magic is, after all, the manipulation of extremely unlikely events – among other more boom/flash effects. Magic can create good and bad luck, miracles etc.
Modern technology is rather delicate – the effect of a chip or a logic board deciding to go on the blink at a particular moment is more catastrophic than say, one hinge on a door. The door may work, if poorly but few computers can handle a logic board crash.
As to what magicians believe about how they affect technology on an individual level – well, that’s theory.
IMO – there shouldn’t be a way to keep technology safe from magic in this particular game. It starts to get too WoD and munchkin if you’ve got the magic/technology détente going on. In this game, if you want magic, you give up telephones and iPods. If you want iPods, you give up magic.
And, magic isn’t necessarily stronger than tech – because the strength of magic depends totally on the strength of the person using it. Sure, in the books we see Dresden slinging uber-powerful shields around but remember, he’s the crem-de-la-crem. Most players, starting out, will not be nearly o powerful, and may never achieve that level of strength.