Fraud is what the government decides it is, the governments have deemed this to be fraud.
Telecom companies don’t necessarily care about this, it’s often the governments who want to tax incoming international calls as an easy revenue source.
I consider it to be relatively harmless but how it is classified depends on the country. India is pretty cheap to call even absent simboxes but they still crack down on the practice for “national security reasons” because it makes tracking people more difficult. The UK (Ofcom) banned them outright for some reason a long time ago but that’s being appealed. In some African countries the laws are pretty vague and do not outright ban them, usually they charge people with “unregistered telecommunications business” or something like that.
Is this really fraud? Is it fraud to offer any VOIP service, or only when it can connect to the phone network, like Skype?
I guess I could see how it might be against the T&C's of the telecom company, to offer a service that undercuts them, but hardly a criminal act of deception.