It’s different audio codecs and data connections which can be changed and adjusted.
Voice over mobile data will benefit from a different type of data compression relative to how data packets are handled in a cellular radio vs a wired internet.
The landline service could be as clear or clearer than mobile data, it just isn’t configured to do so in your case. I have seen VoIP setups using a high quality codec and a handset that can use those frequencies.
Phone companies use different setups that compress to their advantage for many more callers.
I'd not really call it different packet handling (except for some of the earlier, mostly 2G ones not providing FEC at lower layers and delegating some level of error concealing to the codec, as far as I remember):
The main difference is that the bandwidth available was just much lower, so mobile codecs are compressed more. (Satellite phones take this to the extreme – 2.4 kbps is a typical data rate after compression there!)
But so were e.g. international trunk lines; they squeezed a lot more than one voice channel into 64 kbps using compression, silence suppression etc.
> The landline service could be as clear or clearer than mobile data, it just isn’t configured to do so in your case.
An analog landline has relatively little chance of ever gaining wideband support, since that would require swapping out line cards at the provider, and the trend seems to be to get rid of these entirely (in favor of a VoIP adapter in the CPE).
I think I've once used "HD voice" on a "landline" when calling a mobile phone, but that only worked because my home router was actually doing SIP in the background.
Voice over mobile data will benefit from a different type of data compression relative to how data packets are handled in a cellular radio vs a wired internet.
The landline service could be as clear or clearer than mobile data, it just isn’t configured to do so in your case. I have seen VoIP setups using a high quality codec and a handset that can use those frequencies.
Phone companies use different setups that compress to their advantage for many more callers.