Adding content to a page from an external application through service would be a tough job, as you can't do it from the PageService alone. You can inspect what services are called in Sitefinity when you edit a page (with Firebug for example), put content on it and then publish the page. You can try replicating this behaviour by calling the services one by one in your external application, but as I've said it could be hard to do.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items