Ive had this problem aswell...... my 8900 wont connect to the router BUT my girlfriends 8520 is fine!?!?!?!?
If i take the battery out and turn the router off..............leave both off for about 30secs, turn the router back on 1st, put battery back in the phone.......... it SOMETIMES connects when the phone boots back up, but if it doesnt i turn the wifi connection off for 5 - 10 secs and turn it back on and its ok?!?!?!!?!?!?!?
dont know what it is, confusing because only the 8900 does it, and its regular, at least once or twice a day, but the 8520 is fine