Buyback service Gazelle has launched its most aggressive price-lock promotion ever. The service is offering up to $350 for your old iPhone if you lock in a price quote now, and you don't need to send it in until Oct. 10.

This is good news for Apple fans or those who own iPhones since the iPhone 6 is expected to be released by Sep. 19.

Between now and Sept. 9, current iPhone owners can lock in a top-tier price quote at Gazelle.com. The site says anyone who locks in to their quote before the deadline has until Oct. 10 to send in their current iPhone.

Now is the best time to take advantage of this deal, since trade-in values usually drop 20 percent in the 60 days around the introduction of a new phone, much of which taking place 20 days before the unveiling and 20 days afterwards.

This means those who are looking to purchase an iPhone 6 soon after it's announce and then sell their old iPhone should think about locking into a quote now.

Even after locking into the quote, you're not required to send your device in if you decide to change your mind, or if another service presents a better offer, according to the website.

This week, Gazelle is offering up to $120 for an iPhone 4S, up to $205 for an iPhone 5, and $195 for an iPhone 5C.

They're also offering up to $350 for an iPhone 5S.

Once Gazelle receives your device, they completely wipe off the personal data by returning it to its original factory settings. They send out payments to customers through PayPal, email (for an Amazon Gift Card) or issue a check for the cash value of the device.

Gazelle is nation's leading consumer electronics trade-in service with more than 2 million trade-ins processed, and $175 million paid out, as of press time.

The service also pays out hundreds for other devices like MacBooks and iPads.

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