Just received this scam text message regarding a Walmart gift card.  To report these phone numbers, Walmart suggests the following:

If the message was sent from a shortcode (example 123-4), it is likely legitimate and you can reply ?STOP? or ?OPT-OUT? to stop receiving further messages. However, if the message comes from a regular phone number or you are still suspicious, forward the message to ?7726?.

You'll then receive an automated message from your wireless carrier, asking you to enter the phone number from which the spam text was sent. This will allow mobile carriers to take appropriate action, which might include investigations, warnings and blocking of senders who have been reported by end users as sending unsolicited or fraudulent messages.

This is a well-known scam

Dear Walmart shopper, your purchase last month won a $1000 Walmart Gift Card. Click her to claim: www.WmartEnter.com