OK, personally if I wanted to do this, I would still do it all on Arduino. I would use a wifi enabled Arduino (wifi shield or something like the diamondback or hydrogen from DIY sandbox) and then either:
1. serve a webpage from the arduino that enables you to control the light from a browser on your phone
2. use an OSC app like TouchOSC and send OSC to the wifi arduino to control the light
There are tutorials for doing exactly these things on the DIYsandbox website, and the Asynclabs website and the Arduino forum.
This leads me to wonder why you need RFID too? Isn't an on/ off button on the phone interface enough? If you really want to use Max, then you are going to have to follow the advice you were given and examine your serial issues.
If you mention the problems you get with the code I gave you then I/ someone else might be able to help you, though you might want to head over to the Arduino forum.