Apple started selling contract-free iPhone 6 and iPhone Plus online on Tuesday both in its retail and online stores in the United States.

9to5 Mac was the first to report the news Monday as its sources said Apple decided to sell unlocked iPhones to boost sales. Users will be able to use any SIM and switch carriers anytime they prefer with these contract-free devices.

Those, who will order unlocked iPhones will have to wait three to five business days for shipping. The SIM-free iPhone 6 price starts at $649 for the 16GB version while the iPhone 6 Plus starts at $749 for the same storage capacity. Prices are similar to the contract-free units being sold by T-Mobile, according to Mashable.

This is not the first time that Apple sold unlocked units; it did the same scheme for its iPhone 5 and iPhone 5s. It was delayed this time, probably because of the high demand and low supply.

Apple will report its full-quarter sales for the latest iPhones on Jan. 27, but forecasts say that revenue is already at more than $63.5 billion with at least 10 million units sold during its opening weekend.