Infrastructure and service are different layers
A major network operator runs radio infrastructure. An alternative provider may obtain network access through commercial arrangements and supply its own billing, plans and support. Carrier-owned prepaid brands can also have distinct terms from the parent's retail service.
Some arrangements are hybrid, and corporate acquisitions can change the picture. Do not force every provider into a simple “owns all towers” or “uses one host forever” description. Check the actual product and current provider information.
Shared infrastructure does not mean identical features
Data priority, hotspot, roaming, video treatment, compatible devices and support channels can differ. A host's coverage map or postpaid benefit list should not replace the alternative provider's own terms.
A provider that offers network choices may require an account operation or a different SIM to change them. That is not the same as a phone automatically using every network simultaneously.
Compare the line you would actually receive
Check supported devices, activation method, payment period and cancellation conditions. Test local performance where practical. For a legacy line, ask whether an old network arrangement still applies before buying replacement equipment.
Use the provider's own account tools for support and number-transfer credentials. A host carrier's store may not manage another brand's account even when the phone uses related infrastructure.