자답이네요..

일단 타블릿인지 폰인지를 구분해서 따로 디자인하면 될것 같은데,

해당 API는 없고 아래의 소스로 구분 가능합니다..

Virutal dpi means dots per virtual inch. For example, the htc desire hd's real width is 2.21 inches, but its virutal width is still 2 inches, the galaxy tab 10.1's real width is 5.35 inches(portrait orient), but its virtual width is 5 inches.

int portrait_width_pixel=Math.min(this.getResources().getDisplayMetrics().widthPixels, this.getResources().getDisplayMetrics().heightPixels);
int dots_per_virtual_inch=this.getResources().getDisplayMetrics().densityDpi;
float virutal_width_inch=portrait_width_pixel/dots_per_virtual_inch;
if (virutal_width_inch<=2)
   {//is phone
   }
else
    {//is tablet
    }

http://developer.android.com/guide/practices/screens_support.html

안드로이드 개발하려면 한번쯤은 꼭 읽어봐야 할 내용이죠.