Before flying with my poles, I did a lot of research on hiking websites, and people's success at trying to carry them on was pretty inconsistent (no big surprise). So I've always checked mine, which fit diagonally in my larger (24") suitcase.

Poles can be disassembled for cleaning and lubricating so, as others have mentioned, you can also take them apart for packing. Look online to see if the manufacturer has disassembly instructions, or ask at the shop where you bought them. If they're Lekis, look here:

http://www.leki.com/trekking/faq.php