Low/bad signal on iPhone 4 after upgrading to IOS 6

Question

I recently upgraded my iPhone 4 to IOS 6 (from 5.1.1 it had before), and since then I'm having lots of signal troubles: the signal is always low and unreliable, and the iPhone continuously switches between 3G and GPRS (also draining the battery in the process). Internet access is almost unusable, and sometimes I can't even make or receive calls.

I'm in Italy, my carrier is TIM; however, this is not a carrier problem, and is unrelated to the actual place I'm in: I'm having these signal troubles in the very same places where I had full signal strength before the IOS upgrade.

I've been searching around for a while, and looks like this is quite a common problem; various solutions have been proposed (including downgrading to IOS 5 on the assumption that this is caused by some bug in IOS 6), but no agreement has been reached about how to actually solve it.

How to fix this?

Answer 1

The only solution that actually worked was a full factory reset:

• Make a backup of your iPhone using iTunes.
• Using iTunes, perform a full reset of the iPhone.
• After the iPhone reboots, disconnect it from iTunes and go through the initial setup.
• Connect the iPhone back to iTunes.
• When asked by iTunes, choose to restore the backup.
• If applications are missing after the restore, perform a full sync to have them re-installed.

I also called Apple support, and they confirmed this is a known and common problem when upgrading to IOS 6, and a full reset is the only way to permanently solve it.