Update the SMS sending limit instantly (2/2)

This commit also shortens and simplifies the preference summary text
considerably.

Patch set 2  : Slight rewording
Patch set 3  : Another minor wording change

Change-Id: Ic7ed803e22ead8c41346a66edc6db65cee93c39a
Merge commit 'f124f6cab9ea53ccee6508b074a1c51fb2de09c4' into jb2-PIE