I need somebody to test something for me!
PLEASE ONLY TRY THIS IF YOU'RE SURE YOU UNDERSTAND WHAT YOU ARE DOING.
I am checking to see if I've fixed the issue of sending long SMS messages, but as far as I know this could crash the RIL entirely.
I only have a Verizon Galaxy Nexus ("toro"), not a GSM Galaxy Nexus ("maguro"), hence why I am unable to test this.
You'll need to download this file: libsec-ril.so - Google Drive
Copy it to the following location (keeping the same filename): /vendor/lib/
MAKE A BACKUP OF THE CURRENT "libsec-ril.so" FIRST.
You'll need to remount /system as read/write to do all of this.
After verifying that the permissions are set to 644 and the owner and group are set to root, reboot. If you're able to make a connection to the cell towers, try to send a long text message. I'm talking 300+ characters. If it sends successfully, then I fixed this issue.
Make sure you test this on FML only.
Other ROMs probably have a different fix for the issue already in place, however my attempt at fixing it would fix the issue for good and does not require patching Android itself.