“how about” gives a suggestion or asks someone to consider a
possibility.
How about taking a walk after dinner?
How about expanding on this idea in the second paragraph?
How about [banning / a ban on] anonymous letters to the
editor?
You want to be a doctor?
How about a foot doctor?
You want to be a scientist?
How about a microbiologist?
You need something to put on your website? How about some games and puzzles?
“how about if” is common.
How about if I put it in the oven to warm until we’re ready
to eat?
“how about” can give such a strong suggestion that it
borders on a command, especially when there is a feeling that one is being treated badly.
How about a little privacy?
How about a little courtesy?
How about some respect?
“what about” may express a concern about something not yet
explained or not yet made known clearly.
It expresses a desire for more information, often about something
troubling.
I’d like to start a business. But what about the costs?
I’d like to buy these shirts. But what about refunds?
What about animation on DVD? Doesn’t it compress poorly?
Are some pesticides safer than others? What about pest control devices?
This product seems to work well at the office. But what about when you go home from
work? Or what about when you are on a trip?
That said, the two expressions are frequently interchanged:
What about expanding on this idea?
How about pest control devices?
[All examples are modified versions of examples found by
Googling “how about” and “what about”.]
CJ