If the problems are due to Android 2.1 then surely Android 2.2 would fix those. However, if it is a hardware defect or 3G Data network issue then no. Here is info from Virgin Mobile USA Discussion board.
Here are some benefits you can get with the upgrade to Froyo:
-The most important benefit of FroYo is the speed improvement. This can vary per device but overall the device gets noticeably faster and systems become more stable.
-Various improvements to device UI, such as new 3D gallery, camera interface, calendar, etc,
-Cloud to Device messaging that allows users to send apps, web pages, directions and other objects directly to your phone.
-You can now install selected applications onto an SD card to save precious internal memory space
-Latest Google Applications, including a new Android Market with new look and feel.
-Some apps can be updated automatically
-Phone lock by PIN and password added
-Remove wipe and lock support
These features will not be implemented in the M910 FroYo upgrade:
-Adobe Flash support
-Portable WiFi hotspot support
-Live wallpaper
-Car mode application