Verizon Wireless has slashed prices on the Palm Pre Plus and Palm Pixi Plus just one month after the operator dropped the mail-in rebate for the devices in favor of instant online discounts.

When Verizon first got the devices, it was offering the Pre Plus and Pixi Plus for $149.99 after a $100 mail-in rebate and $99.99 after a $100 mail-in rebate, respectively. Both deals required a new two-year customer agreement.

The operator is now selling the Pre Plus for $49.99 and the Pixi Plus for $29.99 – no mail-in rebate required – with a two-year contract. Verizon also dropped the $40 subscription fee for the devices’ mobile hot spot app for both new and current customers, allowing subscribers to use the devices as a personal Wi-Fi hot spot for free. The deal includes 5Gbs of data per month.

A spokeswoman for the operator said the deal was part of Verizon’s Mother’s Day promotions and she said the prices would go back up eventually, though she declined to provide a specific end date for the promotion.

Sales of the webOS devices have been disappointing and the company is working to reduce carriers’ overstocked inventory. The company shipped 552,000 more units than it sold during the third quarter and its fourth-quarter sales are expected to be half that of its third-quarter sales.

In a conference call with analysts, Palm Chairman and CEO Jon Rubenstien said the launch of the company’s most recent devices with Verizon failed in part due to poor training of sales staff.

Palm’s webOS platform faces significant competition from other device platforms, most notably Google’s Android operating system. Recent data from comScore shows that while webOS’ U.S. market share slipped form 7.8 percent in October 2009 to 5.7 percent in January 2010, Android’s market share rose 153 percent to comprise 7.1 percent of the domestic smartphone market.