Sorry for the double post...I just realized you can prevent the iPhone from connecting to free wifi connections with Settings > Wifi > Ask to Join Networks off. If living in a big city this could be useful (I live in the sticks and didn't think of it, hehe :/)
The new iPhone update comes out next Wednesday. Some fear that it may slow down the iPhone 5, but they're soft-pushing it to it anyway with a daily popup (hoping you give in to get you to spend more cash, possibly another instance of planned obsolescence similar to how even typing on the iPhone 4 became extremely laggy after iOS7.) Here is how to prevent the update from downloading without jailbreaking and safely, which prevents the annoying daily popup.
1. If you're unfamiliar with your router, Google [router brand] [model number] "instruction manual."
2. Follow the instructions to log into your router from your computer. It's pretty easy for most routers - don't get intimidated at this step!
3. Block the following sites:
These are the servers the updates download from.
Note: iOS updates will only download from wifi, not cellular data. So by blocking it at the router's level, you've prevented the update from even reaching your phone while still being able to access the internet without using data. Neat! One more step:
4. If you frequent places that have free wifi, the update will still download when you visit them, but only if you spend a huge amount of time there (this update's going to be large, 2-3 GB in size.) You circumvent this entirely, though, by forgetting those networks (Settings > Wifi > Tap the active network > "Forget This Network".) This may not be ideal if you have an extremely limited data plan and like to get work done using the wifi at a library or other public location where you have no control over the router's permissions.
You might, however, try asking them if you can block the servers on their router. It's iffy, but if you present it politely they may let you. You can do this from your laptop without needing to connect anything to the router - you don't need a physical connection to log in, and many routers use only the default admin password, which should be in the online documentation for that router.
If the update does manage to download because of a stray free wifi connection your phone passes by (unlikely with the size of the update,) you can delete the iPhone update by going to Settings > General > Storage and iCloud Usage > Manage Storage > Select the update > "Delete Update."
I realize this is long, but once it's set up, you shouldn't have to delete the update any more often than once in a long while, if at all. You'll be free of those annoying popups and can save $700 on a new phone.
Susan the Wombat
p.s. I wrote this myself and I'm not good with technology, so please correct me on anything you like and/or offer suggestions for improvement )