That's what I suspect too. I've sent an email to Niatic on the first day this happens but didn't hear anything back from them. I might switch away to public mobile if this persists as I found a similiar price at another carrier. Unforunately my phone...
Thanks. I have been having the same issue since this morning. I was able to get in only once after a while in the morning. Then it doesn't work again for the whole day. After tethering through a friend I was able to play. Oh well. I've sent the email...