> So you built your business entirely relying on third-party services.
I'm going to have to disagree with you there. Neither Twilio nor Stripe are in the same business line as RollCallMe and thus are offering services, and thus not competing, therefore they have an incentive to keep prices down in order to attract more customers. I cannot speak for Stripe, but Twilio has lowered their rates in the past and does a wonderful job in regards to both technology and customer service.
Yes, there are no technical barriers to entry into this one-service industry, aside from knowing a Rails person who can wire up the app, but time-to-market, initial pricing and the potential for add-ons that can engage more users and augment the revenue streams give them the advantage. Choosing Twilio gives them that advantage.
Not a rock-solid app by any means, but one that's needed and doesn't compete directly against more mature and properly funded platforms.
Great idea. I wish them good luck.