Hi, I just read this post and i think i ever encountered this problem before.
when i try to install my hsp56 micromodem using pctel-0.9.6, my modversion.h also not present. It is because the location 0f your modversion.h file is different from your linux source file.
maybe you can try to create the symbolic link from your linux source file to the directory of your modversion.h , maybe somewhere on /usr/src/linux.
This method solved my error, although now I have another error and STILL I cant install it. sigh.
well, if you solved your problem, may be you can try to look at my post
and give a hint or help.
Good luck