When we released Echofon for Mac, we were excited to provide a free, ad-supported version using targeted ads within user timelines. This seemed like a great way to show ads without being too obtrusive. Twitter has since launched their own ad system which displays sponsored tweets in search results and may soon do so in user timelines.
Understandably, Twitter has asked app developers to remove ads from the timeline. To comply with their request, ad placement will be modified in the free version of Echofon for Mac. We are now placing ads at the top of the timeline, with a different style of background. This is so that it is clear they are advertisements, separate from your timeline.
You can read about Twitter's ad system and their decision not to allow apps to place advertisements within the timeline in this Twitter blog post