Is carrier diversity essential, or can two SIMs on the same network be enough?

Two different carriers usually provide the best redundancy because the whole point of dual SIM is to avoid a single carrier outage affecting your site. SIMs from the same network still have some value—for example, if one service has a different APN, billing arrangement, or priority, or simply for operational simplicity—but they do not offer the same geographic and network diversity as two different carriers. If you can't get two different carriers, you can still gain resilience by confirming both SIMs use independent paths on site and by testing failover under realistic outages. In that scenario, plan tests that mimic real outages and verify the router switches as expected and that critical services stay reachable. It helps to document which APNs and plans are used and ensure monitoring can alert you if one SIM becomes unusable.