To me, that’s fine. Can I make a suggestion, though? IMHO, the punctuation can affect the impact with which the message hits the reader as well. How about:
Too busy to join the line?
Just click and you’ll be on line!
Thank you both for your kind assistance.
So I would say that the words "be in line" in the original slogan do not quite denote that the customer need to be in the queue.
I very much agree with both of your suggestions.
The question mark suggested do carry an impact.
The words proposed "get in line" do clearly indicate that the customer need to join the queue.
Once again thanks to both of you.