Good & Lightweight Rated 4 out of 5 stars
This is a nice, simple, elegant add-on that doesn't bloat TBird. I have 2 suggestions for you to consider should you get to updating/enhancing: (1) Allow the user to leave some fields blank (e.g. sometimes you don't have a number handy but know the person can look it up); and, (2) Offer the ability to send as plain text or as plain+HTML.
Good & Lightweight
Thanks for the comments - the blank fields is deliberate, and is an attempt to make people fill out the message properly (prevents 'Jack called' with no details).
The plain text and HTML was discounted as HTML (other than being prettier) didn't add anything to functionality