For things like that, I like the approach Iago has proposed some time ago. The question then was about an underwater breathing spell, and he proposed to do it as a skill replacement ritual with a shift value of a resources roll required to buy decent scuba gear (based off the table on YS322). Base duration would be 1 scene.
I like this, because it is pretty easy. You can just google the price range for the gear you want and then set up the ritual at the appropriate level. Since you can put thaumaturgy spells into enchanted items, this also applies to them.
So a set of good walkie-talkies for 4 people should be in the 500$ range, making it a fair (+2) ritual. Further away, you will need something a lot stronger, but I don't really know radio communication that well beyond the basic walkie-talkie. I think there are ways to get a lot further, which are not really portable. Of course, this is where the magic comes in and makes it work on a smaller item (maybe for another shift of power?). Or maybe you send the magic messages through the nevernever to shorten the distance. This would especially be interesting for a third party to intervene.
Cellphones might be a bit tricky, but doable. Cellphones don't create a direct connection between the two devices, they need celltowers. You could cover you city with a grid of magical celltowers that will bridge the distance between two parties. Once you have your grid up and running, you can create magical cellphones that connect to the grid and therefore to the other magical cellphone in the net. Depending on how you set it up, you can actually call a single person or communicate with everyone connected to the net. This idea would probably work best as a background thing without any power in itself. As an aspect on the wizard, you can have all kinds of things happen in the net (ghost in the wire for example).
Uh, or maybe a layline phone, tapping into the grid of (powerwise insignificant) laylines around your city to send the messages around. "Cellphone reception" would depend on how close to a layline you are, and there might be blindspots. But the actual enchanted item could be a set of "cellphones" for everyone, making it a 3-4 shift enchanted item, I think.