my signal has dropped to almost nothing after restoring to a fresh 4.2.1. I used to get full 3g in my house and now its "searching" or just a couple bars of E
Also seeing this issue, except mine won't fall over to Edge unless I do so manually (via the "Disable 3G" setting).
Here's my post on the Apple boards:
I'm having a similar issue with my new iPhone 4 (w/ 4.2.1)... It continually cycles through the following sequence:
AT&T / 3G
AT&T / No Data
Searching?
Searching? 3G
AT&T / 3G
(loops?)
Here is a video of the cycling. Note the iPhone 4 is just sitting on a coffee table in my house:
"h tee tee pee"
dl.dropbox "dot"
com/u/7186070/ip4_fw421_searching.mov
(I can't yet post links here...)
Also worth noting, I just got the iPhone 4 and I updated it to 4.2.1 right away. Previously, I had a 3GS which did not exhibit any of this behavior in the same location in my house. Also, my girlfriend still has a 3GS and has FW 4.2.1 without these issues. I have a video of her phone in the exact same location taken just after the clip above and her phone maintains 3-bars / AT&T / 3G the entire time.
I picked up the iPhone 4 while out of state over the holiday weekend and did not observe any of these connectivity issues, in fact the 3G throughput of the iPhone 4 was significantly better (consistently got >4 Mbps down / >800 Kbps up) than what my family members were seeing with their 3GS models.
I believe it is a baseband issue introduced with the 4.2.1 update for iPhone 4, but I also strongly believe there is some tower component to this problem (ie, software revision at the tower or configuration).
Like others here, I also performed a restore to 4.2.1 through iTunes and setup my phone as "New" and I continue to see the behavior. The phone is unusable in my house unless I manually disable 3G. As a final data point, when I'm able to maintain a 3G connection long enough in my house I get the following throughput from Speedtest.net: 1863 Kbps down / 543 Kbps up.