We recommend that you consider your use case as well as the scale of your application when managing your Number Pool.
Sending International Messages
If your application is sending messages internationally, we recommend purchasing phone numbers in each country you will be sending messages to. If Twilio does not provide SMS-capable phone numbers in a specific country or if there are no phone numbers in your number pool that match the same country as your recipient, Twilio will select an alternate phone number in the Service. Therefore, we highly recommend including phone numbers with global reach for fallback purposes. For example, if your Number Pool for a Messaging Service only has SMS-capable phone numbers that supports domestic SMS (such as US Toll-Free numbers or Ireland mobile numbers), your application will run into an error when trying to send a message to Germany. In this case, we recommend including a US local phone number, or you can find other phone numbers with global SMS capabilities here.
Sending Messages using a Short Code
If you are using a short code to deliver messages, the Shortcode Reroute feature in Copilot will fallback to using a long code when you attempt to send messages to unsupported carriers. Therefore, make sure you have at least one long code in the country you are reaching along with your short code.
Scaling your Service
Short code numbers can send messages at the rate of 100 messages per second, while long code phone numbers can send at the rate of 1 message per second and toll free phone numbers can send at the rate of 3 messages per second. We recommend you add numbers to your number pool depending on the amount of messages you will be sending and the urgency of your messages. You may see messages sitting in the "accepted" state when the application hits the bottleneck.