Just got my 2750n this morning and it is so much better than the BT kit on BT Infinity so I'm really pleased. However I have plugged in a usb stick and was hoping to use the advertised iTunes/DNLA function to share music but there is nothing under USB Application except general setting/users/disk status and shares. Does anyone know how to set this up?

I didn't realise the 2750 had any media server functions.

From the product web page
iTunesâ„¢ and DNLA Server
For even more media sharing, NAS on the Vigor 2750 supports a built-in iTunes server; this means that media files (movies and music) stores on the router's memory can be accessed by iTunes, installed on any of your network's computers. Simiarly, a DNLA server is also supported. DNLA (Digital Living Network Alliance) is a technology supported by many electronics companies to make the sharing of media files across a network easier, including TVs, DVD/PVR products, games consoles and handheld devices.

...but how?

It's a typo on there right now unless there's a * by those listings, those were added to the 2130 (effectively the 2750 without the VDSL modem) with the 1.5.x firmware, which the 2750 doesn't have yet. Once the 1.5.x firmware comes out for the 2750 it'll have those features