There is one particular app I am in love with at the moment. It is called Red Stamp. The app allows you to make invitations and photo cards directly on your phone and send as a text message. You could even post to Facebook.
It is a great tool that is easier than just text over a photo. There are several options for invitations. It is a great option for quick thank you texts that show a little more effort that just the written word.
This is a great tool to have in your arsenal for when you need to send that special someone a special something and all you have is your phone and 30 seconds.