If you aren’t familiar with the three little dots and the fact that they are a type character in their own rite, then I recommend checking out the very informative Wikipedia entry.
Hold down the period button until the secondary keys appear.
You can even do this while the keyboard is in alphabet mode. Just hold down the numbers key, don’t let go, drag onto the period, wait until the alternates appear, drag onto the ellipsis and let go. Bingo! You are right back to the alpha keyboard.
(After testing, it seems the dragging to/from both keyboard sets works only in certain settings. It definitely works if you click into the number layout and then drag and release.)
I love ellipses…
“Three little points of suspension…”