Well, the jurisprudence here is that if the ad is 'unreasonable' (like a LCD TV of 99 EUR; the famous 'Otto case') the customer could have reasonably known it is probably a mistake.

But in this case, Nokia confirmed the advertisement to be correct.

The number of people affected is not relevant in relation to whether one of them can sue or not. It'd be a civil lawsuit, which is filed on individual basis, so one customer could start such for themselves.

The lawyer involved I believe is rather interested in creating jurisprudence which, even though we don't have common law, is nevertheless interesting.

As stated anyone can consider a civil lawsuit for anything. The fact someone is getting sued in a (civil) lawsuit says nothing about guilt or innocence.

I'm not sure whether they already paid, but given the response of allowing full refund, I'd say so.