I use my Tesla app frequently and it works fine in the USA whether roaming or not. I am currently overseas and while my phone works to make calls, and text, it will not "reach" my car. Nor will other apps I have work, like Nest, Chamberlain and Wink. Perhaps I have a setting wrong? It says it is using GSM / UMTS; others are LTE/CDMA and Global. None work.