I know little about the web capabilities of smartphones, but I can describe how GSP renders media objects and maybe that will help.
The first thing to figure out is what kind of HTML (and perhaps plug-in) is required to play the video in the phone's browser. Some types of videos are never going to play because the browser can't do it and there isn't a plug-in for it.
Assuming you can come up with a snippet of HTML that will play a particular video, the next step is to create a HTML template in galleryserverpro.config that targets this HTML to a particular browser type. I can help you with this step. GSP uses ASP.NET's capability to sniff the browser type to send the desired HTML to the right browser.
Gallery Server Pro recognizes client browsers using the .browser files located in the machine-wide %SYSTEM%\Microsoft.NET\Framework\v2.0.50727\Config\Browsers directory. If your particular phone's browser isn't listed, you'll have to add it. I have never modified this file so you'll have to Google it rather than ask me. (If you are on .NET 4, modify the path accordingly. Note that .NET 4 includes updated browser files that include iPhone recognition, so you might have better luck using this version.)
Good luck.
Roger Martin
Creator and Lead Developer of Gallery Server Pro