There r devices like E52 and N97 that operate at Quad-band GSM (850/900/1800/1900).
However, when u search for devices using "Advanced features" and select "Global roaming support", these devices r excluded.
Can someone explain that?
Both the phones you listed are quad-band gsm. I am not sure but I think they are excluded from that list because even though they are quad-band gsm, the E52 is only dual-band 3g and the N97 it only tri-band 3g. This just means that the phone will work globally on the gsm network but not always on the 3g networks.