You'll need to use managed code.  See RIL_GetDriverVersion in MSDN for reference.  I've also attached a C# class which wraps this call.  In MSDN, the major,minor versions are returned in the Low and High Word of the return value.  Since the RIL version's format is xx.xx.xx.xx, it appears that each byte of the unsigned long which is returned contains a version number. I've tested the code on a MC70 with a GPRS radio and it appears to work.

Horst, Talk to Dave Mohnke.  Thanks, Eric

One possible way (maybe) is to read the version from the RIL DLL - You can embedded version information in a DLL, so if its there you can read it. SymScript has commands to read the info  - if embedded in the DLL.

Check out the "WanState" tool on the ECRT site. http://compass.mot.com/go/332353468  If you start this executable with a /w command line argument, it will write a bunch of radio info to the registry and a text file. You might want to try running this during each boot of the device, then your .net app would just need to read from the registry or the text file.  Below is a sample of the data provided. I'm sure the support position is similar to symscript. Probably not officially supported in a production environment, but it works.
 

[HKEY_CURRENT_USER\Software\Symbol\wan info]

"BSP Version"="90.34.01"

"Ntwk Conct Time"=""

"Data Call Status"="No Connection"

"Voice Call Status"=""

"IMSI"=""

"SIM Status"="Not Available"

"RIL Version"="01.01.05.05"

"Radio Config"="Sun 27.04.2008"

"Radio FW"="REVISION 02.050"

"IMEI"="358355010005532"

"Radio Model"="HC25"

"Radio Mfg"="SIEMENS"

"Signal"="0%"

"Network Status"="Not registered"

"Network"=""

"System Type"="GSM"