Different Android versions have different versions of web browsers.
The base Android browser is based on WebKit, but some manufacturers like to roll out their own custom browsers, which makes the problem even worse.
The base browser can be manually updated by installing this, but obviously you cannot rely on it, unless your website is running in a fully controlled environment.
http://caniuse.com/ can help too, although it is not a substitute for testing on the actual devices.
There's a dozens competing standards (heh) in the IoT world, and it's entirely justified because nobody knows what a matured universal API should even look like. While stuff like Hue, Wink and SmartThings have solid ecosystems that aren't going away anytime soon, I'm still going to trust an open project like HomeAssistant to handle the logic controlling them.
As sudonim87 already said you should start with Phonegap. Ionic (http://ionicframework.com/) is great as far as I had to work with it and what you're planning to create. They offer a very nice and easy to lern 'getting started' guide. Have fun with it :-) !
Thanks for the reply. I think I may have worded it wrong. I want to be able to send SMS messages and/or iMessages normally with this app, and be able to see who sent a message to the user. Something like this: https://play.google.com/store/apps/details?id=com.client.SMSAnsweringMachine&hl=en but for iPhone.