You could share PSDs with Dropbox, DM screengrabs, or email PDFs containing sketches for your proposed iPhone app, but why not collaboratively share those latest ideas with Upstage, the latest project from the folks who’ve brought you Boxcar? Upstage is another recent project gunning to simplify iOS developer’s needs to share and collaborate ideas frictionlessly online. Providing frames for popular iOS devices, you’re allowed to upload screenshots to create a series of screens that can be shared with clients and coworkers. I didn’t see any markup tools inside the app for quick sketching or circling, and developers will have to keep in mind the various resolutions for their devices if they wish to upload their designs. While the service is in public beta, you can help the Upstage team improve, add features, and iron out bugs by giving the service a trial run.

[Upstage via ReadWriteWeb]