> Do you mean voip wholesalers?

No, to become a voip providor, you neet to place servers in a hosting
center, a large Internet connection, E1 ISDN PRI connections from a PSTN
switch and DDI numbers from a PSTN providor. This could be BT og Telewest
for instance...

In many countries all the voip providers is connected to the same PSTN
provider.

Regards