hello.
Accessing the Web Services directly requires the mobile device to process all the data that is returned from the web services, which in most cases results in slow performance.
Another major consideration is that mobile networks are typically more expensive and slower than a standard internet connection. and also the major issue is memory In most cases this is more information than you require.
Solution is Multi-tier Web Application and its advantages are.
You can test the application without using a mobile device or emulator.
You do not have to deploy anything to the mobile devices.
Almost all mobile devices have browser capability.
ASP.NET will automatically render the appropriate markup language for the device.
Hope its clear to you.
Regards
D