abook does not provide a multiline read/write area and won't display a multiline text... in a nice way.
Anyway you can "force" it by asking your terminal to input a litteral newline. You can do that using Control-V followed by Control-J (but it may be something else in other terminals like: Control-V <Enter> ?) This will actually store the multiline information. But don't expect a nice display and text edition from abook (nor you should expect a valid output when it comes to export, since most of the built-in output export filters are for format which would break easily on newlines).
