Before I go on and share what I've found so far, a few qualifiers: the following is based on my personal observations and evaluation. It is not scientific, and your mileage may vary.
These tests were conducted at various places in Los Angeles, CA. I used a Verizon iPhone running iOS 4.2.6 and an AT&T iPhone running 4.2.1 for testing purposes.
In addition, the Verizon iPhone had no bumper, but the AT&T phone did -- although, in call testing with and without the bumper, the results were almost identical for the AT&T iPhone. The bumper seemed to make no difference, except where noted below, especially during data usage testing.
Okay, enough of that, let's get to it.
Form Factor and Usage
The Verizon iPhone is basically exactly the same outside as the AT&T version. The main obvious external difference is that unlike the AT&T iPhone, the Verizon iPhone has no micro-SIM Card slot on the right side. In addition, the black strips that break up the iPhone's stainless steel antenna ring have been arranged slightly differently and one more has been added to the mix. Other than that, they are basically identical in all external respects.
Internally, as evidenced by the recent iFixit Teardown, things are a bit different. However, those internal differences don't really impact daily use, at least for me, so they are not really an issue.
The only thing that may be a factor for the Verizon iPhone is that reportedly the antenna has been redesigned after the unfortunate "antennagate" issues with AT&T iPhones. True or not, no amount of holding the device at any kind of angle or with any kind of grip allowed me to produce the antenna signal strength issues reported on the AT&T iPhone.
However, without the bumper, my AT&T test iPhone 4 did exhibit the signal strength issue insofar as the signal strength level dropped one or two bars. So, it seems the Verizon iPhone doesn't need the bumper, but the AT&T version does. (Your mileage may vary on this, as some testers have reported both the traditional cellular attenuation of the "death grip" along with some Wi-Fi degrading from the two-handed "death hug.")
As both devices run Apple's iOS, they also work the same. When I first got the phone, registration was accomplished via iTunes, and then after about 15 minutes, the phone itself was activated. The one difference is that the Verizon iPhone had an iOS update available that brought its iOS version to 4.2.6. Although, as I got mine early, it's possible the Verizon iPhone will ship to the masses with 4.2.6 already installed -- still, be sure to check for updates when you connect yours to iTunes for the first time (it should check automatically, but it doesn't hurt to be sure).
Another difference between the two devices is that on the Verizon iPhone you have the option of turning on the Personal Hotspot feature. This is located in Settings> General> Network. As I'm not paying for the additional feature at the moment, something that will cost you another $20/month for 2 GB of data, I didn't get a chance to test this option.
Other than that, iOS on both devices behaves as you would expect it to.
One area where AT&T was often superior was data speeds -- that's consistent with the tests done by our sister site. Based on testing using the Ookla Speedtest App, I had average data speeds of .94 Mbps down and .48 up for the Verizon iPhone and 1.8 Mpbs down and .82 up for the AT&T version. However, in terms of the number of areas where 3G data was actually available, Verizon's network fared better. I had full 3G access in twice as many areas with the Verizon iPhone as I did with AT&T.
Also, while AT&T had better data speeds overall in areas where coverage was available, the perceived speed in which pages loaded in Safari was almost identical, at least to me. I don't have an explanation for this except that perhaps Apple has managed to squeeze some performance boost out of Safari with iOS 4.2.6? Further exploration is warranted in this area.
Testing data speeds during a call is not possible with the Verizon Wireless iPhone, so I did not try. You need to use voice or data.
For some, this might be a big selling point for choosing the AT&T iPhone over the Verizon one, but for me, at least in this testing and as a Verizon customer for over a year using other devices, it has been a non-issue.
This is where the iPhone on Verizon shows significant improvement over its AT&T counterpart. During my testing when making calls with both phones in exactly the same location and conditions, the Verizon iPhone connected calls faster and they were clearer than the AT&T version.
In addition, during my testing no calls were dropped while using the Verizon iPhone; I experienced dropped calls on at least three separate occasions with the AT&T iPhone.
To make things harder on both devices, I drove along the freeway and made calls during the drive to test the phones' ability to keep a call going while moving. No surprise, the Verizon iPhone kept the call going and did not drop once during three passes. AT&T's iPhone dropped twice, but curiously, the third time it maintained the call and did not drop.
So, in my testing, the Verizon iPhone was superior when making calls in almost every situation. Sadly, AT&T's iPhone did not fare as well.
Based on what I experienced, I would have to say that Verizon has a winner with the iPhone 4. With a few limitations, it performed more reliably than its AT&T counterpart. As someone who has been waiting for many years for the iPhone to come to Verizon, I'm happy to say that the device lives up to all expectations.
Sure, it would have been nice if the iPhone had been equipped with an LTE chip to run on Verizon's 4G network, or if you were able to make voice calls and also maintain a data connection, but those are not dealbreakers for me. Plus, the added benefit of being able to make calls, talk reliably without dropping and general service availability definitely makes the Verizon iPhone a worthwhile purchase.
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