How can dial a modem phone number from an IP connection?

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http://serverfault.com – I have Cisco router in a remote location. I have attached a modem to the aux port of the router. The problem I am facing is how do I dial the modem's phone number from my computer in my house that uses a cable internet connection? I do not want the modem connected all the time since the phone line will be used for calls also. (HowTos)