Operating system name and version: Slackware ; Debian wheezy ; Rpi debian wheezy
Version of smsd: 3.1.15
Smsd installed from: on slackware - sources+slackpkg; on debian and R pi - package repository
Name and model of a modem / phone: DX USB Tri-band GPRS Modem with BenQ M32 GPRS module
Interface: USB (PL-2303 USB<->UART)

I have instaled smstools on several computers ...
Slackware 14.0
raspberry pi debian wheezy
debian wheezy

but on all I can not see (find) RESETMODEMS=/usr/sbin/smsd_resetmodems

so there is no such file anymore ? or how ?

RESETMODEMS is a custom script which depends on the system. There is no general or sample script available in the package.

For example, in some system there are several modems and sometimes one of them freezes. In this case RS232 and external power supplies are used. Freezing does not happen very often, but when it happens, only mains off/on helps. Because of this, the system has an AC switch with USBIO interface, which is controlled by custom C software. When the issue happens, alarmhandler is called and it sets up the "panic" flag. The cron job sees the flag, and calls init.d script to stop smsd, reset modems, and start smsd. This is because the smsd cannot stop and start itself.

oh , I see ...
so we can use USB , RS232 or Parallel ... interface with some relay to power cycle our external modem if there are any
(there are lot of howto using relay , uln2003 uln2008 .... transistors ... "power cycle dsl modem , switch ...etc )
but what if it is modem with "internal" power - I mean getting power from usb port ... ?

can you give some example script ?
"sets up the "panic" flag. The cron job sees the flag, and calls init.d script to stop smsd, reset modems, and start smsd"

I mean how this "panic" is set and checked from cron ... etc