Three considerations that should be made before implementing MobileConnect are:
Long and Short Codes are not available for all countries. Long codes are local phone numbers that can be used for sending SMS messages in some countries, while short codes are special numbers that can be used for sending SMS messages in other countries. However, not all countries have long codes or short codes available or supported by MobileConnect.
Inbound messaging only works with local Long or Short Codes. Inbound messaging is the ability to receive SMS messages from subscribers in response to outbound messages or keywords. This feature only works with local long codes or short codes that match the country of the subscriber's mobile number.
Not all countries are supported by MobileConnect. MobileConnect relies on mobile operators and aggregators to deliver SMS messages to different countries, but not all countries have these services available or supported by MobileConnect.
NTO would not be charged by mobile operators directly for messages, as they would pay for message credits or bundles through Marketing Cloud billing. Opting in for messages can be done via inbound message or other methods, such as web forms or APIs. Reference: https://help.salesforce.com/s/articleView?id=sf.mc_moc_mobileconnect_overview.htm&type=5