[thfuran]

Cell phone audio traditionally only covered 300Hz-3.4kHz before being lossily compressed down to 4kbps (or sometimes higher, depending on network, load in that service area, etc). That is complete shit. Recently, there have been other protocols adopted with greater bandwidth (all the way up to 7kHz, which is still several khz short of covering all the content of speech, but considerably less terrible) and less compression, but if you have audio that's actually good and not merely passable, it's probably because your phone is actually transmitting audio as voip, with a much better codec then is used for cellphone audio transmitted over the standard channel.

[vel0city]

G.711, the standard encoding for home phone systems since they went digital, is usually filtered at 300–3400Hz as well. Chances are if you had a home phone in the 80s or 90s it was filtered at 300-3400Hz somewhere along the path.

[lxgr]

And the history of that filtering even predates digital lines, due to frequency multiplexing: https://en.wikipedia.org/wiki/L-carrier

[lxgr]

Ironically, you've got a better chance of getting acceptable quality on mobile-to-mobile calls these days than when calling from a landline:

The big mobile carriers actually have VoIP interconnects preserving wideband audio, while connecting to an (especially smaller) landline carrier might still involve a circuit switched path (going to the physical location of the area code dialed, too!) that inevitably forces everything through a 4 kHz, 8 bit bottleneck.