When you’re testing with Twilio, it works well for small-scale sending and receiving, but it doesn’t really offer a simple way to simulate hundreds of users replying back at the same time. Most of the SMS testing tools you’ll find are built for bulk outbound sending only and don’t handle 2-way traffic simulation in bulk, which is why you’re hitting a limit with your current setup.

If you want to properly test at scale (like 500+ users sending replies), you generally need either:

• A simulation environment where you generate fake MO (mobile originated) messages programmatically, or

• A platform that’s built for real-world bulk SMS and 2-way traffic handling, instead of just dev-level testing.

This is where an aggregator platform makes sense. Instead of building a custom simulator, you can use a provider that’s designed for high volume and 2-way SMS flows. One of the better options out there is Africala. It’s built specifically for bulk messaging at scale, supports 2-way SMS, and gives you delivery reports and analytics that mimic production usage. That way you don’t just test sending, but also realistically test how your system processes hundreds of replies at once.

So in short: Twilio is fine for initial dev, but if your goal is bulk user simulation with both sending and receiving, a service like Africala is going to be much more practical.