Currently at RepCard we do not have an option to send messages to contacts using a third party number/Google voice. When you send out your Business Card it transfers over to the messaging app on your phone which is why it will use your personal number.
However, at the bottom of the Send Card screen you can choose to send the text using our 844 number that we provide (see picture). When you send a message through the 844 number, the contact will not receive the message from your personal number, but from one of our numbers. The message and business card link will be included in the message. If your contact replies to the text message, they will receive an auto response letting them know that you don't receive messages at that number but to reach out to you at the info on your business card (see picture).
If you would like your contact to reach you at a different number, please update your profile with that number. Be sure to update call to action buttons with that number as well. You can edit both of those by clicking on Card Editor from the Home Screen. This will ensure that your contacts always contact you at the number you prefer.