If you want to add a personalized note on the invite, click on the tiny blue icon on the right. (entrepreneur.com)
Finally, select «Phone» from the list, which uses a circular blue icon. (android.gadgethacks.com)
Once you've made it out of the first act, you'll begin to accumulate sidequests called «Favors» that are marked with blue icons on the map. (kotaku.com)