Some of a telco’s biggest customers and biggest vendors are other telcos.
MVNOs operate on MNO networks. MVNOs have agreements on access and usage to use MNO networks. MNOs also have agreements with other MNOs to roam on each other’s networks. These are called access charges and access revenue
MVNO networking is more common now even with the big providers where the roaming is "free" because they lease or trade bandwidth.
Some of a telco’s biggest customers and biggest vendors are other telcos.
MVNOs operate on MNO networks. MVNOs have agreements on access and usage to use MNO networks. MNOs also have agreements with other MNOs to roam on each other’s networks. These are called access charges and access revenue