I wouldn't waste my time developing on a Blackberry when you can have the power of .NET Compact Framework on Windows Mobile phones. Blackberries are a Yuppie toy. You need to learn Java to develop natively on the Blackberry unless you use something like http://www.flowfinity.com/developers/blackbird_faq.html which enables an ASP.NET app to run on a Blackberry as a web based application. BUT you cannot access the local filesystem of the Blackberry using this method. Have a Windows Mobile device and you have ASP.NET/.NET Framework and access to the filesystem to store time data until the user is back in the office to upload the information or use a web service to send the data.