it sounds like somethings interfering with you router signal... make sure the frequencies on your wireless phones are not the same as your router. my linksys was 2.4 and i had the same problem. i dont understand why.... linksys makes great products and is very well known... i am not using an offbrand router that came with my Fios and i havent had any problems at all... go figure...
you can do a HARD reset on your router and reconfigure all your setting. hold reset for 30seconds, while still holding reset, turn the unit off for 30 seconds and turn in back on.
did you have trouble with everything before the firmware upgrade? the new firmware might not like you wireless cards.
make sure you are using a encrpted signal. and also change your password and username on your router other than admin/password
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