Unless you’ve been living under a rock the past few years, you know the talk now is all about apps. I believe Cisco has a secret crystal ball, perhaps stored in John Chambers’ lower desk drawer, because apps were available for Cisco IP phones many years before all the buzz started. Here are a few resources you might want to consider. (NOTE: Use your good judgment and discretion, and do all your research. Just because I like an app doesn’t mean it’s going to be perfect for you.)
To start off, why not just write your app? If you want to do so, then you should get the Software Developer’s Kit (“SDK”) from Cisco.  Another great resource is the Cisco Press book, Developing Cisco IP Phone Services: A Cisco AVVID Solution.  While enormously powerful, you might find that writing your own app just isn’t your ball of wax. That’s okay — I’m right there with you! So, here are some nifty apps that my students and I came across over the years that you might want to look into.
If you’re in healthcare, then you might want to check out Extension Inc.’s middleware . This app lets you access data in your Electronic Medical Records (“EMR”) and Practice Management (“PM”) systems from the IP Phone. The mobile altering features work particularly well with the WiFi-enabled IP phones. No more waiting around to find out when labs are done; just get an alert. 
If you operate in the federal space, you probably know that there’s a requirement buried somewhere within a Homeland Security Presidential Directive (“HSPD”) for federal installation mass alerting. IPCelerate,  a Cisco partner, developed some text messaging and voice alert apps that might help fulfill this requirement. I was particularly interested to learn you can schedule tones, announcements, and messages for future or recurring delivery. I can think of several times we planned downtime and would have liked to send a scheduled announcement out five minutes before the start of the maintenance window just to remind the users in case they forgot (or ignored) the email from earlier in the day.
If you work in a legal office, this same company also makes IPSmartSuite, a product that handles Client Matter Codes for incoming and outgoing phone calls. You can also switch CMCs in the middle of a call if multiple matters are discussed on a single call. There’s even a lookup utility in case you can’t recall the CMC.
In addition to these apps, there some really neat things you can do with Computer Telephony Integration (“CTI”). Say a Cisco instructor uses a UC500-series appliance at home. These Smart Business Communications Systems do offer a couple of ‘connectors’ that enable CTI.  They work with applications like Microsoft Dynamics CRM, Windows, and Salesforce.com.
Finally, no discussion would be complete without mentioning Cisco Unified Widgets.  These FREE, yes FREE, apps are available from Cisco. I fell in love with the Visual Voicemail app for Unity Connection. My users seem to like the IP Phone Designer. Being able to make their own ringtones and backgrounds really trips their trigger.
So there you have a few apps to get you started. If you have any you particularly like, please let me know — I’m sure others out there would be interested.
 Disclosure — while I have no interest in the products offered by Extension, I have worked with a few of the developers in the past.