Pros
Top SF/Silicon Valley startup company with a great product. Market leader in providing unique and programmable mobile telecom solutions via PaaS API. Developing new technology/services ahead of the curve. Huge growth over the past 3 years and definitely a company which will only continue to grow and be successful. Product out-performs competitors. Well known among tech industry and more and more outside the tech industry. Great opportunities, room for growth, and plenty of money.
Cons
Cons mostly revolve around your opinion of SF/Silicon Valley startups. Fills all of the tech startup cliches: catered lunches/dinners, over abundant company swag, manufactured quirkiness, heightened sense of self importance i.e. "we're changing the world", an anti-corporate corporation dichotomy, located in SOMA, it's a "fun" place to work, 90% of employees under 30 years old, required wholesale dedication to company "vision", etc. Basically, if you like the culture and fit in than there are no cons. If you don't feel as though you would fit in things might be a little tougher though you could say the same for any company.