You should never use a personal phone number for offers, you will get lots of spammy phone calls. There are a few options you can use other than your personal phone number.
Google Voice - Follow instructions for creating Google Voice numbers. You can make and receive calls with Google voice.
Skype - You can use Skype to make toll free calls, other calls will require you to add money to your skype account.
Pinger/Text Free App
- Download to your mobile device (tablets too) and register for a phone
number in your area. You can make and receive phone calls and receive
sms text messages from these numbers. Easy to get a fresh phone number
by logging out and creating a new account. You have a limited number of
minutes for each phone number.
For iOS: https://itunes.apple.com/us/app/text-free-free-texting-app/id399355755?mt=8
For android: https://play.google.com/store/apps/details?id=com.pinger.textfree.call&hl=en
Please read for more info on kindle and Google Play
Burner phones - these are real cell phones that can be purchased almost anywhere, usually no contract with pre-paid minutes.