Yes, I always use my mobile. Most landline companies have priced themselves out of the market as far as calls are concerned.
Except if you're in a spot where:
a) There's no mobile coverage
b) Broadband speed is so slow that if you want to use VoIP, you better make sure no-one's doing anything else on t'innernet in your house
You have failed to grasp what is being said here. Put simply, calls from a mobile are free because of the generous quota of minutes automatically included with any contract phone. No point in using a landline with its rip off connection fees and high call charges. No mobile coverage areas can be sorted through the use of a sure signal device with Vodafone or your router for EE. Either selection appears to work at pretty low broadband speeds to give a full signal to your mobile.
That leaves the landline predominately for a broadband connection but handy to have if the broadband goes down to maintain a voice connection to the outside world..
As for VoIP, if your broadband speed is particularly slow, voice quality will indeed be poor, even more so if other traffic is using the connection at the time of the call. You can do something about that too by bonding two or more broadband services.. Not a cheap option, but then you will get an un-contended, symmetrical service to give you a faster speed and a superior VoIP service..
VoIP provides all features without paying surcharges. Reasonably priced call bundles are now available giving free calls to landline numbers and mobiles.
So your issues can be sorted without suggesting otherwise.