What would a "Call of Cthulhu" prop site be without the obligatory Western Union telegram?
Click the picture below to get the full-size, high resolution version and then save that to your hard drive.
If you just want to bang out a quick and dirty telegram, open the blank telegram image in a graphics program, add a layer with your message text in a typewriter font, and print.
If you want something a little more realistic you'll need some yellow paper and a word processing program. Open a new 8 1/2" by 11" document and put the blank telegram image on the top of the page. Then use the bottom half of the page to type out your message, again with a typewriter font. Print out the document, cut the page so the blank telegram is on one sheet of paper and your message text is on the other, and then carefully cut out the strips of paper containing your message text. Then use a glue stick to attach the strips of text to the blank telegram sheet.
Tada! An almost instant telegram.
Here's a rough guide to how your document should look if you're using the more involved technique I described above.
Here's an actual Western Union telegram to give you an idea how it should look.