On the windows mobile properties for the form, you can select the Form State to be maximized. There are also dll imports you can use to hide the Start Icon and SIP Buttons.
Below is the code I use to hide the Taskbar and SIP Buttons
#region SHFullscreen
#region FullScreen Imports
[DllImport("AYGShell.dll")]
private static extern Int32 SHFullScreen(IntPtr hwndRequester, UInt32 dwState);
public const UInt32 SHFS_SHOWTASKBAR = 0x0001;
public const UInt32 SHFS_HIDETASKBAR = 0x0002;
public const UInt32 SHFS_SHOWSIPBUTTON = 0x0004;
public const UInt32 SHFS_HIDESIPBUTTON = 0x0008;
public const UInt32 SHFS_SHOWSTARTICON = 0x0010;
public const UInt32 SHFS_HIDESTARTICON = 0x0020;
#endregion
private void SetFullScreen()
{
#region FullScreen
WindowState = FormWindowState.Maximized;
SHFullScreen(Handle, SHFS_HIDESIPBUTTON);
SHFullScreen(Handle, SHFS_HIDESTARTICON);
SHFullScreen(Handle, SHFS_HIDETASKBAR);
#endregion
}
#endregion
Hope this helps you :)