Although rooting this phone used to be a little more difficult, its actually pretty easy now with all the advances the devs have made. It's a easy as downloading a small program to your computer and then connecting your phone to the computer. The program on your pc then roots the phone for you with one mouse click. It's easy and it's foolproof.
Just follow the directions.
http://forums.androidcentral.com/lg...ck-root-sons-korhal-root-utility-1-0-1-a.html
Once the phone is rooted, go to the android market and download a program called Root Call Blocker. This will block all those bothersome calls for you.
The pro version is about $5.00 but the free version should work fine for you. I have tried a few others but this is the only one that actually works (at least on my optimus), and it works really good.
Because it works at the system level the phone never even rings at my end. The person calling might hear half a ring on their side before getting cut off. The app is a thing of beauty in how it works but you have to be rooted.
So download Sons of Korhal to your pc and follow the directions to root the phone. Then download Root call blocker trial from the market.
Once done, you'll also have the option to do a lot of other things with your phone since it's rooted, but that's a whole other thread.