I have seen some sites they are using google text ads and yahoo text ads on all pages, i think its voilation of TOS , as i know we can only do non contextual advertisement with google ads... tell me i am right ? or i can also use google ads with yahoo ads on one page and on all pages ?
In the "TOS" as far as i remember "contextual advertisement is not allowed". So its a violation of the TOS. (Ofcourse i might be wrong we shall see) Btw , i have searched forums and saw that it is Againts the TOS... (Am i correct or wrong still suspicous...)
Both are contextual ads systems - Google do not like any other contextual ads on a same page. You can implement them on different pages of your site but never put them on the same page. From Google's policies page: https://www.google.com/adsense/policies Seriously ppl, all your initial questions are all there if you spend the effort to look into it. Google is still the best place for these kinda things.
As long as both of them arent displayed at the same time, you can alternate them. I emailed google about this already.