It is VERY easy to search in the MIT Galllery for app examples. Use the MENU on the Designer to go to Gallery and search for dial

This adapt will need to be adapted to your purposes It uses Balls, not Image Sprites and then you will have to add the code to actually dial the number .... search the gallery for 'dialer'
When you get it working, please consider posting the blocks and / or aia here in the forum so others may benefit.