Is there a version of Eric Prydz's number 1 hit in the UK Call On Me
that is instrumental-i.e no vocals? Where would I be able to buy it?

Hi Squall55

I spent a lot of time looking for the answer to your question, but I'm
not sure it is exactly what you're looking for so I've posted this as
a comment.

I found a discussion about this subject on a German music forum:
http://www.tranceunited.com/forum/list.php?thread=1211

I translated the threads using Google's language tools:
://www.google.com/language_tools

The last thread translates to:
"In the current B&J mix in their mp3 shop there is another new
instrumental valley version without those "call on me" samples, calls
itself "Apollo & Zeus ? Call Me (Instrumental Valley Mix)"."

The B&J the thread refers to are German DJs Blank & Jones. Their MP3 shop is here:
http://www.deejay-net.info/blankandjones/index.php?language=en

If you go to DJ mixes and Blank and Jones you'll find the track here:
http://www.deejay-net.info/blankandjones/product_info.php?cPath=22&products_id=123

Note that the website says "All tracks in this mix are previously
unreleased" so you are unlikely to get the track elsewhere.
Unfortunately, the available audio sample does not feature this track.

So who are Apollo & Zeus? They definately have something to do with
Eric Prydz as there is a "Eric Prydz - Call On Me (Apollo & Zeus
Remix)" available. And why is the track listed as "Call Me" and not
"Call On Me"? For these reasons I have not posted this information as
a final answer. If this is the track you are looking for do let me
know.

Best regards

Paultoon