These people need to be put in jail. The problem is that this phone number might not even belong to them. I get this same spam message sent using a different number each time I get it.
If you get text spam, report it to the FCC. Hopefully they are doing something about it.
You can fill out the form here:
http://esupport.fcc.gov/complaints.htm
Tell the FCC they need to do something about this! Mobile phone text spamming It is a major problem! Don't expect the carriers to help much because they are making lots of money off of it for people who have to pay for every spam text!
Changing you number may backfire. Your new number is someone else's old number. You'll be tormented by the previous owner's pests.
The gift card is a scam. They ask for a credit card number to confirm you are the person they are looking for or to pay a small shipping and handling fee. They take that number and go wild, spending $$$$ of your money.