This could be the case for the internet, but AFAIU not (so far) for the calls or SMS. No roaming fees means that if you have a Bulgarian SIM and live in Denmark

This could be the case for the internet, but AFAIU not (so far) for the calls or SMS. No roaming fees means that if you have a Bulgarian SIM and live in Denmark and you call a Bulgarian number, you will pay as if you were in Bulgaria. But they can still tax you more when you're calling to the Danish or any non-Bulgarian number. Anyway, for people who rather use internet than make phone calls, this can be a good deal indeed.