Skype for iPhone lets you send texts, make both voice and video calls, and has a nice-looking interface. Unfortunately, it's missing a key feature, and a bug I found makes the app unusable under specific circumstances.
Updated for the iPhone 5's larger screen, the most recent version of Skype looks great with a home screen that lets you view your contacts and gives you buttons across the bottom of the interface for navigation. You can add contacts through the Skype directory, save a phone number directly, or import numbers from your iPhone contact list. Besides contacts, you also have buttons across the bottom for Messages (IMs); a dial pad for calling phones; and a My Info button where you can add a photo, check your Skype credit status, listen to voice messages, and turn on call forwarding.
I found various issues during my testing of the app. Some are merely features that don't exist yet for iOS (but do on Android), while others are pretty serious bugs.
When using Messages, you are only able to send messages to one other user; you cannot send a message to a group (something you can do easily with iOS 6 iMessage). But using an Android phone, we were able to start a group chat with my iPhone, and I was able to participate -- I just couldn't initiate one myself. This is a feature that will probably come soon to the iPhone version, but it's worthy of noting.
One of the main reasons you use Skype is for free video calls and the feature works nicely, but it has one serious bug. If you're on a video call, and someone makes a regular call to your phone, it stops the video call and lets you answer the call to your iPhone -- nothing wrong with that. But when you hang up, Skype opens to the Messages screen with no way to exit (buttons at the bottom are no longer available). The only way out is to return to your iPhone home screen and force quit the app. If that weren't enough, the video call continues for your Skype friend (until you force quit), but there's no way for you to know that your camera is still transmitting. This is a serious bug I was able to recreate that must have been overlooked, so I hope Skype will update the iOS app soon with a fix.
Even though it is lacking group chat features, and has the serious issue mentioned above -- for sending messages, video, and voice calls, and staying in contact with Skype friends -- the app works fairly well. Just hope that you don't receive a phone call in the middle of a video call or you're going to be stuck with no way out.