If you already have an original iPhone and want to upgrade to an iPhone 3G you're going to have to purchase a new handset and extend your AT&T contract for another two years.
Since there's no upgrade path to the iPhone 3G (Apple hasn't offered upgrades in years) you'll have to sell your original iPhone to a friend or in an online auction and purchase a new 3G handset from either AT&T Wireless or an Apple store. Original iPhone owners that purchased in June of 2007 are one year into their existing two-year contract and will have re-up for two more years. AT&T requires a new two-year contract for customers with existing iPhone contracts that want to upgrade to the iPhone 3G. Note that this isn't a contract extension, you just get a new two-year contract when you purchase the new handset.
AT&T rate plans for iPhone 3G are as follows:
Individual voice plans:
- $39.99 – 450 minutes
- $59.99 – 900 minutes
- $79.99 – 1,350 minutes
- $99.99 – unlimited minutes
Unlimited 3G data costs US$30 per month.
Family Talk voice plans:
- $69.99 – 700 shared minutes
- $89.99 – 1,400 shared minutes
- $109.99 – 2,100 shared minutes
- $149.99 – 3,000 shared minutes
- $199.99 – unlimited shared minutes
Family Talk plans can have between two and five lines and each line after two must add $10 per month to the rates above. Unlimited 3G data access costs US$30 per month, per phone.
Update: AT&T has not yet announced their SMS rate plans for the 3G iPhone. It has been rumored that individual and Family Talk rate plans will no longer include SMS messages and that AT&T will charge US$5 per month for 200 SMS messages and US$20 per month for unlimited SMS messages. This is still unconfirmed.