Open the text-messaging app on your smartphone, touch the microphone icon, and try dictating the imperative “Please call me, David.” as a text message. You should expect to get “Please call me David” instead. Speech-to-text technology in these apps often does not treat pauses as anything special.

You might type a period to terminate the sentence, but you might miss the need to insert the comma where it is needed.

Now, imagine three things:

1. You are sending the text message to a man by the name of David.
2. He knows you as John Smith.
3. He has heard rumors that you might go by a different name.

Now consider two different messages that this man could get, depending on whether you inserted a comma after “me” in your imperative message.

“Please call me David.”

This is asking the recipient to refer to you by the name “David” (instead of by “John” or “Mr. Smith” in our imaginary example).

“Please call me, David.”

This is asking the recipient to telephone you.

Conclusion

If you want someone to refer to you by the name “David”, then send a “Please call me David.” text message.

If you want someone to telephone you and that person’s name is David, then send a “Please call me, David.” text message.