What are the differences between the AT&T Wireless data plans for the iPad? What are the differences between the plans for the iPad and the iPhone? What is the difference in total cost of ownership?

For those who are less than thrilled with the iPhone arrangement in the US -- which requires a two-year contract with AT&T Wireless and is locked to the carrier -- it was a pleasant surprise that the iPad is available both unlocked and without a contract.

It is worth noting that the low-end models, starting at US$499, are only equipped with Wi-Fi and cannot connect to a 3G network, whereas the higher-end models -- priced from US$629 to US$829 -- have 3G capability (and Wi-Fi and A-GPS).

It also is worth noting that even though the high-end 3G-equipped models are not locked, the hardware does not support the Verizon CDMA 3G network nor does it support the 1700 MHz UMTS/HSDPA frequency used by T-Mobile for 3G in the US. Essentially, even though the iPad is not locked to AT&T Wireless, the device itself is not hardware compatible for 3G with other US wireless carriers. However, it should operate via the slower 2G standard over T-Mobile.

AT&T Wireless in the US, again without a contract, is offering two 3G data plan options for the iPad -- 250 MB of data transfer for US$14.99 a month and unlimited data transfer for US$29.99 a month. Should one reach the 250 MB limit for data trasnfer on the entry-level plan, AT&T provides the option of purchasing an additional 250 MB of data transfer for US$15 or switching to the US$29.99 unlimited plan.

AT&T doesn't offer a 250 MB data transfer option for the iPhone, only unlimited data for US$30 per month. A voice plan also is required, whereas the iPad does not have a requisite voice plan or mobile phone capabilities.

The least expensive two-year total cost of ownership for the iPhone 3G and an iPad equipped with 3G capability and plan are compared below:

	iPhone 3G (8 GB)	iPad (16 GB)
Device Cost:	US$99	US$629
Voice (450 Minutes):	US$39.99	N/A
Minimum 3G Data Cost:	US$30.00†	US$14.99†
Monthly Usage Cost (w/ Voice):	US$69.99†	N/A
Monthly Usage Cost (w/o Voice):	N/A	US$14.99†
Total Minimum Cost (2 Years):	US$1778.76†	US$998.76†

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

Naturally, one can argue that it is not fair to compare the iPhone, which provides phone service, to the iPad, which does not provide phone service, as just about anyone buying an iPad likely will want to buy mobile phone service from somewhere, and this is not included in this comparison. This iPad service plan also only provides 250 MB of 3G data for the iPad as well, whereas the iPhone plan provides unlimited 3G data.

A truly frugal iPad user, however, could buy the even less expensive US$499 model and not pay for 3G service at all, opting only to use Wi-Fi at home and elsewhere when it is available and perhaps pairing it with an inexpensive mobile phone and plan for an even lower two year cost of ownership.

Ultimately, this comparison does illustrate the substantial difference that required monthly service fees can have over a two-year period.

Also see: What are the differences between the AT&T Wireless voice/data plans for the iPhone 3GS and the iPhone 3G? What is the difference in the total cost of ownership?