Pretty damn simple.
The one thing most people hate is leaving a message on a recording, or just a simple busy signal, or no answere. What is something that cell phones have that land lines do not have?
Fricken Text messages.
Most phones these days come with caller I.d. on them these days, so the displays are not the issues.
I’m pretty sure that if the text addition was free, it would get used on a really regular basis. Downside is that advertisers would hammer out millions of messages at one time. So there would have to be a fee for the text message add on so it would be illegal to use someone’s privately funded text messages up.
I can only imagen the tiny pc’s people would try and push to sell to accomidate the texting and people with large fingers, and extended message storage for the times when you are away for a while.
It would also have to allow the line to be able to text and call at the same time. This way so the kids don’t hold up the line, and so you can get messages while talking.