Apple has begun selling the iPhone 3GS contract-free in the US as it prepares to introduce a new model iPhone, perhaps in June.

An internal Apple memo tells retail store staff, “Effective immediately, customers purchasing iPhone as device only at full price are no longer required to have an A&T account or provide a form of ID.”

Apple is selling the iPhone 3G and 3G S contract free for $499 (8GB 3G) and $599/$699 for the 3GS 16GB/32GB respectively.

Customers are limited to purchasing one iPhone per day contract-free, up to a maximum of ten units can be purchased by each customer, Apple says.

Customers must still Jailbreak their iPhone In order to use the it on other networks

Note that technical reasons mean the 3G radio inside the iPhone does not support high speed data networks of any operator other than AT&T, which uses a different 3G technology.