For years it was suspected that ITFS numbers had funny issues. Maybe they could not be called from Hotels or from some mobile providers. With a large call center in the USA that had Mexico toll free it became very evident with millions of calls. We quickly had to work with local Mexican cartriers to get a “Domestic ITFS” or In-Country Toll Free”. The format was slightly different and the numbers worked from everywhere. The locals who called the number said the format was better. We have many other carriers where we get “Domestic ITFS” or In-Country Toll Free” because they work and they cost per minute is lower.