eBay is looking to help lessen the financial burden on those looking to make the switch from their current device or carrier to Verizon Wireless for the CDMA version of Apple’s iPhone 4.

eBay announced a two-week promotion in anticipation of the release of the iPhone 4 on Verizon this week. From today through Feb. 22, eBay Instant Sale will offer cash guarantees of $200 for select functional smartphone models and up to $450 for AT&T iPhone 4s.

The money people garner from the sale of their existing devices could help pay the subsidized price of $199 for the Verizon Wireless iPhone 4. It could also be used to buy out contracts at their existing carriers, if they are not already with Verizon Wireless.

According to a press release, eBay users can take a $200 guaranteed price on any functional iPhone 3GS, Motorola Droid X, HTC Evo 4G and Samsung Galaxy S Vibrant smartphone models. Customers can also receive a minimum of $200 and up to $450 for the AT&T iPhone 4 during the eBay Instant Sale promotion.

In comparison to what eBay users will get if they go it alone, the current average selling price of a 16 GB AT&T iPhone 4 is $581.62. If they use the guaranteed Instant Sale, they’ll receive $344.

“With the launch of the iPhone on Verizon this week, it’s the perfect time to show our customers how easy it is to trade-in a smartphone and get a great deal along the way. Offering tremendous value and a user-friendly shopping experience to our electronics customers is a top priority for us in 2011,” said Christopher Payne, vice president of eBay North America, in a statement.

To broaden consumer awareness, the eBay Instant Sale smartphone promotion will be communicated through on-site, email and social media marketing and engagement. eBay expects the promotional campaign to generate an estimated 1.2 billion impressions over the two-week period surrounding the launch of the iPhone on Verizon.