I've found that even older speaker docks will often readily accept the newer iOS devices such as iPhones & iPod touch by simply inserting the Griffin charge converter inbetween. Here's a link to the product you should investigate. Seems like it's not carried much anymore unfortunately.

http://www.google.com/products?q=Griffin+Charge+Converter+&aq=f

http://www.ilounge.com/index.php/reviews/entry/griffin-charge-converter-firewire-to-usb-for-iphone-and-ipod/

Useful info in the review section-
http://www.amazon.com/Griffin-Charge-Converter-Adapter-iPhones/product-reviews/B001OI2VGI/ref=dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints=1