Foursquare on Monday unveiled a revamped iPhone app that includes commenting and more advanced photo options.

Version 2.2 will allow friends to comment on your check-ins. If someone checks into your favorite restaurant, for example, offer a suggestion on what to order. Did someone check into a concert you're attending? Let them know where they can find you.

The commenting feature extends to the Web site and from check-in links posted to Facebook and Twitter, Foursquare said. Comments are only visible to friends.

Users will also be able to post more photos, including when posting a tip. "See dishes before ordering them, figure out if a venue looks fun, or easily identify a hard-to-find spot. More info = better exploration," Foursquare wrote in a blog post.

Photo check-ins are only visible to friends and the networks with whom you share information, like Twitter and Facebook. Tip and venue photos will be public.

Several partners are involved in the photo options. Photos pushed to Foursquare from Instagram will be check-ins with photos instead of just check-ins. Sightings on Foodspotting will be check-ins with your food photos, and picplz will be the first service to allow photo check-ins on iPhone and Android.

Foursquare promised a revamped Android app later this week. Versions for WebOS and BlackBerry will be released in January, and other major platforms will get an upgrade in early 2011. An API for developers will be ready later this week, Foursquare said.

Several features didn't make it into this release, but will be included in a future launch, including sharing photos on Facebook and Flickr, an easier way to keep track of comments, and a more useful place to store old photos instead of the history page.

The iPhone app is available for free now in the App Store.