It will always depend on how compliant the service decides to be with laws and taxes. If they want to be legal, they will have to ID you somehow to invoice you "correctly". Doesn't matter if you pay in fiat, BTC or whatever.
Discussion
Interesting. So selling a fax without kyc-ing a customer is illegal?
Is selling a phone card that allows you to make a phone call without kyc-ing the caller illegal?
I didn't say KYC and said ID instead in purpose. KYC is specific of the banking and financial sectors.
In any case, in Europe at least, selling anything online without charging the corresponding sales tax is illegal, at the very least. And any income you make on that sale has to be justified and declared.