Phone Call Alert via GSM Modem

[doub]

Hello,

I would like to implement a mechanism for generating a phone call once a trigger is raised. I do not want to use any third party VOIP providers as I already own a GMS modem.
Does anyone have an idea to get me walking?
Playing a soundfile or reading text is all good - any ideas are welcome.
I am currently using Zabbix v2.0.9 .

Thanks in advance.

[aib]

Take a look on third-party software which can help you to wake up your boss at 3:00am on December, 25th.

[doub]

Aleksey, thanks for the reply.

This is a good post and if I do not find a more suitable solution I will definitely go with that.

My biggest concern is that it relies on unsing the Internet. This means in case our Internet connection goes down we will not receive any alerts anymore.
I was thinking of using our GSM modem but I do not know how to access it in order to establish a phone call. Another option is using our PBX. It is capable of VOIP and fixed line but I do not know how to address it either.