What are the AT&T Wireless voice/data plans for the iPhone 4? What is the least expensive option? What is the total cost of ownership?

Please note that this Q&A compares the plans offered by AT&T at the time the iPhone 4 first shipped on June 7, 2011. Plans may have changed since that time.

A few days before the unveiling of the iPhone 4 -- and a new 8 GB configuration of the still current iPhone 3GS -- AT&T, which is the exclusive provider of iPhone service in the United States, made a significant change to the data plans for the iPhone models. Voice and text plans reportedly remain the same††.

The details are covered by press release, but in brief, AT&T eliminated the previous unlimited data for US$30 a month option and replaced it with two choices -- "DataPlus" for US$15 a month, which provides a mere 200 MB of monthly data use, and "DataPro" for US$25 a month, which provides 2 GB of monthly data use.

Users on the DataPlus plan who go over 200 MB are given another 200 MB of data transfer for an additional US$15 and users on the DataPro plan are charged US$10 per additional gigabyte. DataPro plan users can add "tethering" (connect their iPhone to a notebook for mobile data use), for an additional US$20 per month plus combined data usage over 2 GB.

Somewhat surprisingly, as first spotted by MacRumors, existing iPhone users can grandfather their existing US$30 a month unlimited data plan but tethering is not an option without switching to the DataPro plan. If one decides to switch away from the unlimited plan, it is not possible to switch back either.

AT&T claims that 65% of customers use less than 200 MB of data a month on average and 98% of customers use less than 2 GB of data per month, again, on average and is positioning this change as a way to "make mobile Internet more affordable to more people." For those who are not heavy users of mobile data services, this is true, as US$15 and US$25 are both less than the previous US$30 a month minimum. It also is worth noting that with these plans AT&T is providing unlimited access at more than 20,000 AT&T Wi-Fi hotspots in the US at no extra charge.

However, it presumably will be more profitable for AT&T to provide tiered service or the company would not have made the change. The reported 45% of customers who use more than 200 MB of data but less than 2 GB will either have to pay US$30 on months when they go over 200 MB or switch to the US$25 a month plan for 2 GB of data. The reported 2% who use more than 2 GB of data will end up paying more -- perhaps considerably more -- than they would have with the previous plan (assuming that they are not a grandfathered customer).

The purchase price of the iPhone 4 -- and the new 8 GB configuration of the iPhone 3GS -- can vary depending on your "status" with AT&T as well. New and qualifying AT&T customers are offered the iPhone 3GS with 8 GB of storage for US$99 and the iPhone 4 with 16 GB or 32 GB of storage for US$199 and US$299, respectively, with a two-year contract.

For "non-qualified" customers or those "who wish to buy iPhone as a gift," the iPhone 3GS is US$499 and the iPhone 4 is US$599 or US$699 with 16 GB or 32 GB of storage, respectively. These models still are "locked" to AT&T and require a two-year contract.

The least expensive option from AT&T for either the iPhone 3GS or iPhone 4 provides 450 daytime minutes, DataPlus (200 MB of data), and no text messages for US$54.99 a month. Adding 200 text messages costs US$5 a month, but one conceivably might not be interested in text messaging (or alternately paying 20 cents per text for infrequent use). This does not include AT&T Navigator which "transforms your iPhone into a voice-guided GPS navigation system for traveling across the country and just across town" for an additional US$6.99 a month (US$3 a month less than it was previously).

The least expensive realistic two-year cost of ownership numbers are below. These assume that one is qualified for the iPhone 3GS or iPhone 4 as an existing or new customer:

For intermediate users -- interested in 900 minutes of monthly daytime voice use, 2 GB of data, and 1500 monthly text messages -- the two-year cost of ownership is:

For heavier users -- interested in unlimited voice, 5 GB of monthly data (which would represent a handful of full-length streaming movies a month), unlimited text messaging, tethering, and voice guided GPS navigation service -- the two-year cost of ownership is:

* These are the least expensive prices for new AT&T customers and upgrade eligible customers.

† No prices include taxes or other applicable fees, which can be quite substantial.

†† When checked on the date published (see top), AT&T's website was presenting this plan as US$69.99 per month and Apple's was presenting it as US$99.99 per month (the same price as it was previously from AT&T as well). Apple subsequently changed this on the company website to US$69.99. Consequently, this Q&A is correct as published.

When compared to the previous unlimited data plan, both light and intermediate users save money, and heavier users pay a lot more. Nevertheless, by even glancing at the total cost of ownership over a two year period, it becomes quite obvious that the majority of the cost is tied into the service plan rather than the iPhone itself.