Has anyone completely replaced Twilio with an Android SMS Gateway?

I've been experimenting with using an old Android phone + SIM card as a self-hosted SMS gateway instead of paying per-message fees.

So far I've found a few interesting tradeoffs:

• Local SMS costs are dramatically cheaper.
• Setup is surprisingly simple with a REST API.
• Great for OTPs, alerts, CRM notifications, and internal tools.
• But reliability depends on the phone, carrier, and internet connection.

For anyone who's tried this in production:

• How many SMS/day are you comfortably sending?
• Have carriers ever rate-limited or blocked your SIM?
• What's been your biggest reliability issue?
• At what scale did you decide to move back to Twilio, Vonage, or another provider?

I'd love to hear real-world experiences rather than benchmark numbers.