WHEN WILL PHONE 6S BE AVAILABLE FOR UPGRADE?
Not sure what you're asking. When will you be eligible to upgrade to a 6s? Depends on when you last upgraded and what type of upgrade you got (2 year contract, Edge). When will there be an upgrade to the next device after the 6s? Typically it will be in one year....next September and it would be theoretical the iPhone 7. The year after would theoretically be the 7s. If neither is what you meant you need to be a bit more clear.
I am Eliable to upgrade right now
And I'm looking to upgrade it online as soon as possible but it doesn't give me the option to choose the new iPhone only the old ones
You must call or in to store to get contracts. Are you sure it's cheaper?
Half the price
