In general, any Twilio phone number that supports SMS can be used for two-way messaging with recipients in the same country dialing code (e.g. +1 for US/Canada, +49 for Germany). "Two-way messaging" refers to receiving inbound messages in addition to sending outbound messages. This is covered in detail in Receiving Two-Way SMS and MMS Messages with Twilio.

Twilio's US and Canadian (dialing code +1) phone numbers may be able to receive some incoming SMS messages from numbers outside of the +1 dialing code. However, this is not guaranteed to work in all cases, or at all times.

For outbound messaging, US and Canada phone numbers can be used to send SMS messages to countries all over the world (as can any other SMS-capable Twilio number), however the messaging is likely to be one-way only, and/or appear on the receiving device with a different sender ID than the Twilio number.

As an alternative to SMS for two-way communication, you can also check out the Twilio API for WhatsApp, which facilitates two-way messaging with users in just about every country in the world, with any WhatsApp-enabled Twilio phone number.