The biggest differences between iPhone on Verizon and on AT&T are:
- On AT&T you can talk on the phone and be online (browse the web, send email etc.) at the same time.
- With Verizon, you can use the iPhone as a personal hotspot to create a Wi-Fi base station that allows connecting up to 5 devices.
- The volume and Ringer off switches are in a slightly different location on the Verizon iPhone so existing iPhone cases will not fit.
- Text messages longer than 160 characters get broken up into multiple parts on Verizon's CDMA network. AT&T's GSM network re-assembles them into a single message so it's easier to read.
- Verizon has better coverage over all than AT&T for cell phone service. AT&T's network is faster than Verizon's for data use.[1][2]
These differences are explained in more detail below.
Comparison chart
 | AT&T iPhone | Verizon iPhone |
|---|---|---|
 |  | |
| Usage limitation | Can talk and be online at the same time. | Cannot talk and be online simultaneously. |
| Long text messages | Re-assembles long text messages into one so they're easier to read. | Text messages longer than 160 characters get split into multiple messages so they are a little cumbersome to read. |
| International use | The GSM iPhone works in 220 countries. | The CDMA iPhone works in 40 countries including Mexico, Canada, China |
| Network Coverage | Poor | Good |
| Data transfer speed | Good | Poor |
| Personal Hotspot Feature | Enabled; costs extra | Enabled; costs extra |
Plans and Rates
This chart (click to expand) compares the different plans available for the iPhone as of November 2011.[3]
Personal Hotspot
With the personal hotspot feature, the iPhone can be used as a Wi-Fi base station to connect up to 5 devices to the Internet. Verizon charges $20 a month for this feature and allows 2GB of data use. This fee is in addition to the cost of their data plan. AT&T does not price the mobile hotspot option separately. Their fee is $45 for 4GB of data, which includes data consumed as mobile hotspot or by the phone.
Talk or be online
The two iPhones are designed for different cellular networks - AT&T's is GSM and CDMA for Verizon. A CDMA limitation is that you cannot talk and be online at the same time. That means you can't simultaneously browse or send e-mail when on the phone. The Personal Hotspot feature also cuts off. On a 3G network, incoming calls take priority and interrupt your online connection but in a 2G area, you remain online and the call goes directly to voice mail. Text messaging is not affected by this limitation - you can talk and text at the same time.
Coverage
Several users and reviewers have panned AT&T for poor coverage and dropped calls. Independent reviewers testing both phones have found Verizon's coverage to be better over all. There is, however, a possibility that with a surge in iPhone users, Verizon's network will experience the same bandwidth constraints that plague AT&T.
Speed
Having conducted tests for coverage and speed Wired found that AT&T download rates are 62% faster than Verizon, and AT&T upload rates are 38% faster than Verizon.[4]
4G coverage
As of September 2012, Verizon has 4G coverage in the most number of cities. (see 4G coverage map) However, AT&T supports HSPA+, which is comparable to 4G in terms of speed and is in more cities. iPhone 5 supports HSPA+ and is the first iPhone to do so.
International Use
Globally GSM is a more popular network than CDMA. So chances are higher that your AT&T iPhone will work internationally - 220 countries for AT&T vs. 40 for Verizon.
References
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