If users aren't responding there are one of three possibilities:
When a user does not respond they should be sent an e mail asking for their correct phone number, and which cell phone carrier they are using. Check to make sure the country code is listed, as the country code is required.
If the phone number is different than the one in the system, it should be corrected and the text messages resent.
If the phone number is correct it is likely there is a carrier issue. Sorting out carrier issues is time consuming, and a decision should be made whether to proceed to the next steps.
The number should be checked against the list of of supported carriers by country
If the users country and carrier are supported, look up the local phone number for GeoChat: http://geochat.instedd.org/Home/SharedGateways
Have the user send the message '#ping' to the phone numbers. If there's no response, the user's carrier cannot speak to GeoChat. If there is a response, GeoChat should work.