There is some inaccurate advice given here... 2.4 ghz is the frequency that tends to interfere with wi-fi, not 900 mhz. If your phone is interfering with wi-fi, moving away from 2.4 ghz to eiher 900 mhz or 5.8 ghz will likey solve your problem.
And yes, encrypt your wi-fi one and all, do you really want random strangers in your neighborhood doing whatever the hell they want on the internet under your name?