[mattjoseph]

Yes, you can use developer APIs like Twilio, Nexmo or Plivo to create your own SMS application. Carriers have different ways of identifying behavior they dislike in their network - if you're transparent about what you're doing, follow the rules, and get opt-ins from your subscribers you shouldn't have issues.

The specific limits vary based on a number of factors like volume per period, inbound/outbound ratio and so on, but carriers empowered the short code industry (5 or 6 digit phone numbers) to allow mass messaging to happen on terms they're comfortable with. When you create a short code, you specify what they should expect from you and if they approve you get to send 30+ messages per second.

That said, DIY gets complicated very quickly in this space (hence why we built Locent).