I was thinking about this issue and I have an alternate idea. I want to houserule in my group as seldom as possible and make houserules as simple as possible. Therefore:
For most commercial and civilian applications such as a commlink call, noise either has no effect or stops all function. Devices such as commlinks can handle their Device Rating +2 in noise with no discernable affect to their intended function, but are unable to function above that. The reason why it is noise +2 rather than just noise is that all commerical wireless devices have a combination of noise compensating hardware and software intended to improve signal reception.
Therefore most commerical devices (device 2-3) can handle being in a busy downtown area choked with data traffic (noise 4), but the cheap knockoff you buy from a street vender (device 1) can't handle it.
Why make it all-or-nothing? Because of the digital cliff. Analog radio fidelity degrades pretty gradually in quality as the signal strength degrades, which is why analog radio operators say things like "I am reading you loud and clear" or "Five by Five" and give other feedback for progressively worse reception, whereas your digital cellphone calls are generally either completely fine or suddenly cut off without warning. In the real world digital signals work in roughly this way.
Diagram:
http://upload.wikimedia.org/wikipedia/en/6/6c/Digital-cliff.pngArticle:
http://en.wikipedia.org/wiki/Cliff_effect