Apple on Tuesday began offering at its stores and online unlocked and SIM-free editions of its iPhone 6 and iPhone 6 Plus smartphones, giving an alternative to those who want to avoid being tethered to long carrier contracts.

The SIM-free iPhone 6 costs $649 for a 16GB model, with the price going up by $100 for 64GB and another $100 for 128GB. The iPhone 6 Plus SIM-free model starts at $749 and comes in silver, gold or space gray. Unlocked and contract-free versions for T-Mobile cost the same.

Read next: How to unlock an iPhone | How to unlock an iPad from its network | How to tell if an iPhone is locked or unlocked

Apple charges $199 for the iPhone 6 with a two-year carrier contract from AT&T, Sprint or Verizon and $299 for the iPhone 6 Plus with a two-year carrier contract.

According to Apple:

The unlocked iPhone includes all the features of iPhone but without a wireless contract commitment or a carrier installment plan. You can activate and use the unlocked iPhone on the supported wireless network of your choice, such as AT&T, T-Mobile, Verizon, or Sprint in the United States.

If you don't want a multiyear service contract, or if you prefer to use a local carrier when traveling abroad, the unlocked iPhone is the best choice. If you choose T-Mobile, your iPhone comes with a T-Mobile SIM card already installed. You will need to contact T-Mobile or visit an Apple Retail Store to activate your iPhone.

Apple regularly offers SIM-free smartphones right away in other countries, but in the U.S. there is typically a delay. U.S. buyers of the SIM-free phones can expect broader LTE support when traveling abroad.

The original phones went on sale in September.