After you install SP1 for Visual Studio 2005 or you are using Visual Studio 2008, you will see that you can not find Mobile Web Forms which you can see in Visual Studio 2003.
The reason is from Microsoft development team. They made the Mobile Web Form Templates a separate package and you need to download the package.
Also, you need to read here to know how to install the package, I copied part of content to the following:
One limitation users should be aware of is the Design View in Visual Studio 2008, which is based on a completely new archtecure, does not display ASP.NET mobile controls. However, using these templates you should be able to develop ASP.NET Mobile applicaitons using the Source View just fine.
Once installed, these templates enable users to create and edit new ASP.NET Mobile Web Forms in ASP.NET Web Site and ASP.NET Web Applicaiton project types.
To install these templates download the attachment included in this post, extract the ZIP file, and follow the instructions in the included readme.txt files.
And, the most important is HOW TO SEE the Mobile Form Template after you install the package, see the comment below:
When looking into the issue Ahmad reported, we discovered he was looking at the “Add New Item” dialog in a “Website” project, not a “Web Application Project”. Website projects already have mobile form templates, so these do not apply to that project type. These templates are only for the “Web Application Project” type. To do a Web Application Project you should select ‘File > New Project’ from the menu and then select “ASP.NET Web Application” as the project type. In that project selecting “Add New Item” hopefully should show the templates as pictured in the post. Email me at omark-at-microsoft-dot-com if that doesn’t work for you.