I wonder how many calls made on mobiles are actually essential..? When I had a mobile contract I found myself making calls just to use up all the inclusive minutes available. How many calls could wait until a landline was available..? How many calls are necessary at all..? I often see when I am out and about teenagers (nearly always girls..!) phoning one another up when they're almost standing next to one another. *Why* FFS..?!!
Only if they're actually out when making the calls. VoIP could be a viable alternative if most of the calls are made while they are at home, calls between customers of the same provider (and those where there is a peering agreement) are free at all times and even calls to mobiles are often at a better rate than from the mobile itself. On Sipgate I only pay 10p/min to a mobile whereas on Tesco Mobile it's 20p/min and I have no doubt there are cheaper alternatives as well, although I rarely need to call mobiles from home so it's not a problem for me.
Ivor