The mobile phone number requirement is probably the dumbest thing you could have done.
I understand making it harder for malicious users to take advantage of your service, but you are ruining a lot of peoples potential to develop with your API by assuming they can afford a cell phone.
What about people who dont want to disclose their phone number into your service? Assuming I still want to develop, some phone services do not support shortcodes.
What about companies that develop apps for twitter? They would have to go buy mobile phones in order to text your numbers, or require their employees to do so.
Really dropped the ball on this one. Theres a ton of really useful data that can be derived from the API and now you expect those without phones to actually submit a request and have someone real approve it.