I'm having the exact same issue with my iPhone 4S. Upgrading to iOS 7 was a huge mistake for me as my phone no longer wants to connect to my Netgear WNDR3700. The strange part is that 7.0.2 seemed to auto connect about 50-60% of the time and when it didn't, I could at least join the network manually (after 3-5 failed attempts.) Unfortunately, since updating to 7.0.3, not only will my phone not automatically join my wifi network, I can't even manually connect (by repeatedly attempting to join manually.) I also have noticed that my phone no longer picks up some of my neighbours' wifi signals that I used to be able to see under iOS 6. Weird.
This is extremely frustrating as I now have to be careful when making purchases or updating apps (only have a 500mb data plan.) The really annoying part is that the rest of our devices work fine:
Summary:
iPhone 4 (wife's old phone) - fine (iOS 6.x)
iPhone 4S (mine) - doesn't connect 90% of the time; worked flawlessly with iOS 6.x
iPhone 5S (wife's new phone) - connection issues under 7.0.1, fine under 7.0.2 (haven't updated to 7.0.3 yet)
iPad 3 (mine) - fine under 7.0.2
iPad 4 (wife's) - fine under 7.0.2
Router: Netgear WNDR3700 - using IP reservation based on MAC (tried it without)
Security: WPA2-PSK (AES)
Channel: 2.4 GHz = 9 / 5.0 GHz = 48
I've tried:
- Resetting my phone's network settings
- Resetting the phone
- Resetting the router (which seems to help on the first connection attempt, but not always so it could be a coincidence.)
- Disabling DHCP IP address reservation
iOS 6 worked flawlessly, 7.0.0 to 7.0.1 caused wifi connection issues, 7.0.2 was better, and 7.0.3 rarely connects.