This requires gsmlib, and hence isn't enabled by default.

In order to compile this, first get gsmlib from http://www.pxh.de/fs/gsmlib/
(There are ipkgs at ftp.uk.linux.org:/pub/people/dwmw2/gsmtool/)

Compile it, then add 'gsmtool' to the Opie top-level Makefile, set
GSMLIBDIR to point at the directory where you built gsmlib, reconfigure
and rebuild Opie.

Warning:
gsmlib is extremely and gratuitously bloated. It wants rewriting in a sane
language, without the pointless auto-refcounting structures and crap.
Certainly without libstdc++, glib, or other idiocy.

You need to make sure -fexceptions is in CXXFLAGS after -fno-exceptions. 

I see lots of segfaults with gcc-2.95.2, but I can only get compiler support
for gcc 3.1. When I tried to reproduce the errors with gcc 3.1, I couldn't,
so I no longer care. YMMV.

--
dwmw2