Contactreach has many ways for users to opt in to a campaign though the majority use the "text to number" opt in method. That method requires you to use numbers with the country code of where you'd like to use it. That is because users in a country need to send the campaign keyword to the campaign number. If you're demoing to Africa, for example, but use a US number, users may not be able to receive the Welcome Text Message as they can't send an SMS the US number unless they spend for overseas SMS cost. However, other ways to optin are by letting users fill out the campaign form right away through the form's URL. They don't need to text to the number but they'll receive the messages from the campaign through the assigned number. But if you're using an overseas number in that case, make sure its global SMS-capable. Although in some countries, SMS costs higher than using local phone numbers or toll-free numbers so it would always be best to use local numbers and toll-free numbers if possible.