I've proposed before, that such things should easily be possible, though I suspect that wizards don't really try, because they usually have their stuff figured out when new technology comes out. Most wizards are older than most modern technology anyway, and they can't use it. Wizards like Ana who read up on things, despite the fact that they can't use them.
TV, Radio, Phones and the internet all have one thing in common: there is a data signal, that has to be interpreted somehow. Usually, that is done by electronic devices, but who says it has always have to be that way?
My proposition for a magitech computer was something like this:
You get an optical internet connection, so the magic involved does not mess up the electronic signals. Then you pretty much need to build your magical computer from scratch and teach it how to interpret and code the data you receive and send from and to the internet. Since everything you use on a computer follows a strict protocol, it should be possible to create a magical construct that can do so as well.
To display the data, you can use all kinds of things. A mirror comes to mind as the classic example. Or a bowl full of water magic liquidy stuff. Or a painting where the colors flow around to create the images.
We are going to need input devices as well. Some of the display items can probably be used as a sort of touchscreen. With a magically linked pen, you can write directly on the surface, so you won't need a keyboard or a mouse.
Cars:
I'd thought of a car as well, and I thought the easiest thing to do would probably something similar to Harry's force ring. You put up a windmill or a watermill, depending on what works in your area, and link it to the car, charging up the circular momentum, that you can access through the cars magical buildup. Maybe even better, if you create multiple items that you can charge up and store in the trunk, so when one of them is out of power, you can switch them and use a fresh one, while the others are loading up their power again. Though a car like this might work perfectly, imagine what happens if you drive two tons of magic on the freeway. You would be fine, but any other car would stop working.
Oh, and on a side note: I have had this one idea, where a wizard binds the spirits of a buffalo herd to the steam engine of a locomotive to get it running. The images that come with this idea are just too cool.
Cellphones:
I would probably do it a bit different. I would put up a basic communication spell, and I would create it in such a way, that any wizard can recreate it. The design would have 2 slots, one for the phones owner (the sim card, if you will), and one for an item to link it to another phone to call someone. One advantage is, that you don't have to worry about linking every phone to each other. Yes, you are going to need to carry the stuff around, but I think that is kind of a cool side effect. Plus, none two linked items will be the same, which will preserve the individualism the dresden verse magic has.
