The newest member of the iPhone retailer posse, Sprint, is taking pre-orders for the iPhone 4 8GB for $99 on a two-year “All.Together.Now.” contract, making them the only iPhone carrier with unlimited data plan.  The iPhone 4S will be available at Sprint later.

Customers can now head to Sprint’s website to pre-order either the black or white 8GB iPhone.  The iPhone 4 will be offered until supplies last, and Sprint said that they will do the best they can to deliver the iPhones by October 14 or 15.

“While supplies last, we’ll let you pre-order iPhone 4 online only. (iPhone 4S available for pre-order Friday, Oct. 7). Order today, we’ll charge your card for your phone today and we’ll do our best to get a shiny new iPhone in your hands Friday, Oct. 14 or Saturday, Oct. 15”.

The newly released iPhone 4S will be available for pre-order on Sprint starting tomorrow, October 7, and the price for the new iPhone will start at $199.  The product will officially be available in the market by October 14.

The reason for offering pre-orders for the 8GB iPhone is because other carriers used to only offer the 16GB and 32GB.  Verizon is also offering the 8GB iPhone for $99 by October 13, while AT&T is offering the 8GB iPhone for free but requires a minimum data service starting at $15/month. 2 year contract & new activation required.