I think your comparisons are completely wrong. Is there anything you could do with land lines that you cannot do with mobile phones? No, but there are lots of things email does that Facebook does not do (and vice versa).
Send/receive faxes to/from a dedicated fax amchine, use an analog modem or coupler, connect multiple extensions to the same line, connect an Asterisk box, play DTMF tones into the receiver and have it dial, pulse dial by toggling the 'hang-up' switch...
