I have a UK client that is interested in setting up an internet business selling mobile phone accessories in Switzerland.

Is there much demand for mobile phone accessories in Switzerland and what are the prices like; i.e. anyone know of any internet sites or do most buy from say Germany?

I think there is definitely a market. I paid 25CHF for a microUSB cable which is available for less than £2 on Amazon.co.uk

Yes there is
stupidly expensive (you have to ask??)

anyone with any sense buys from the net already, so your mate would just be wasting there money, especially if your mate is thinking of buying in cheap Chinese junk and trying to sell it here, the kind of people who buy that tat will already be buying it on ebay.