While recently trying to signup for a new banking service that allowed me to tie authentication to my mobile phone, whenever I had the service send an SMS authorization code to my phone I never got it. I had a friend send me an SMS and that arrived fine. I then remembered for a long time I'd not been getting Zipcar SMS messages about extending my reservation. Even though my Zipcar account said I had two-way messaging activated when I disabled and tried to reenable the service I ran into the same problem. Turns out there are two different types of SMS. Regular phone to phone SMS messages and another type known as short codes. A quick call to T-Mobile's awesome support and I found out, unbeknownst to me, a content block had gotten put on my account for SMS short codes. Once removed everything started working again. Yay!