I was very pleased with the clarify of the documentation around the API and was able to integrate the entire set of features for two way SMS into my PHP code in my POS / Booking system within about 20 minutes and then within a few hours I had everything polished and working perfectly. My only gripe is that SMS replies come in in chunks rather than as one single message meaning the receiving code has to re-assemble the messages meaning I had to write extra code to do this as that was not included in the documentation. One other thing was the inability to include spaces in the outgoing callerID as can be done on other platforms. Other than that, they are very well priced and so far I haven't had any problems.