I picked up an original 2G 16GB iPhone off eBay for my mum this week and it came with a cable that I've not ever seen before and not sure what it's supposed to do?

This is it:


What's it for?

Had a bit of a Google and can't find anything about it - saw something similar which said it was a charger lead for an iPod Shuffle 2G but not sure why it's come with an iPhone - unless it's just been included by mistake? It's made with the same connectors and outer materials as the iPhone USB charge cable?

Thanks in advance!