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?

Please note that this Q&A covers the total cost of ownership of the iPhone 3GS and the iPhone 3G in the United States as of June 8, 2009 when the iPhone 3GS was introduced. It remains for "historical" reference.

For the total cost of ownership for the iPhone 4 and iPhone 3GS in the United States as of June 7, 2010, when the iPhone 4 was introduced, see "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?"

The iPhone 3GS -- and the iPhone 3G -- voice and data plans on AT&T Wireless in the US are exactly same as they were when the iPhone 3G was released. The only difference is that data is now required "for the life of the iPhone" for US$30 a month.

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

Originally, for existing iPhone 3G customers, AT&T Wireless would only allow customers who had purchased the iPhone 3G one year earlier to qualify for "standard upgrade" pricing (the same prices available for new customers). However, after some teeth gnashing, AT&T extended the offer to those who had purchased the iPhone 3G before the end of September 2008. Customers who purchased the iPhone 3G after September 2008 generally will not become eligible for the lower pricing until September 2009.

However, readers have reported that eligibility varies and long-term AT&T Wireless customers or those paying for higher priced plans may become eligible more quickly or may already be eligible. For complete eligibility details, existing customers will have to login to AT&T Wireless and see what is being offered to them specifically.

For non-qualified customers the iPhone 3G is US$499 with 8 GB of storage and the iPhone 3GS is US$599 or US$699 with 16 GB or 32 GB of storage, respectively. These prices still include a new two-year agreement.

The least expensive plan from AT&T Wireless for the iPhone 3G or iPhone 3GS provides 450 daytime minutes, unlimited data, and no text messages for US$69.99 a month. Adding 200 text messages costs US$5 a month, but one conceivably might not be interested in text messaging. This does not include AT&T Navigator which "transforms your iPhone 3G and 3GS into a voice-guided GPS navigation system for traveling across the country and just across town" for an additional US$9.99 a month.

The least expensive two-year cost of ownership numbers are below. These assume that one is eligible for the iPhone 3G or iPhone 3GS as a new customer or via "standard upgrade" pricing:

For heavier users -- interested in unlimited voice, unlimited data, unlimited text messaging, and voice guided GPS navigation service -- the two-year cost of ownership is as follows:

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

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

Ultimately, 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.