Having an insulin calculator app on your smart phone can be a great tool to have with you, particularly when you are out and about at a restaurant or in a place where you don’t have access to your normal tools (spreadsheet, calculators etc.). This particularly applies if you are using the pen. There are a number of good apps out there for both iOS and Android. We have used Insulin Calculator for the iPhone by fridayforward, a small app developer with a few apps focused on diabetes. 
Here is a screen shot of the app. It is a simple, intuitive layout that has all you need to do calcs on the fly. All you have to do is have your target rate, corrective factor and carbohydrate factor set as constants, then you are ready to go. It will calc the insulin units based on glucose levels and carbs to be eaten on the fly.
There are others out there, but this is an app that has worked well for us. Even if you migrate to the pump, which does all the calculations essentially for you in the unit, it is always good to have on your phone as a backup. We had a situation where the pump wasn’t working and we had to administer insulin by pen again when we were out. Glad we had it as the insulin math skills get rusty if you have been on the pump for awhile. Easy to get spoiled! Let us know any comments you have on your experiences with any other smart phone apps!