spoof voip to hack into it
In August, Secure Science Corporation warned that hackers can use caller I.D. spoofing to break into the voice mail boxes of T-Mobile subscribers. A U.S. wireless company with 15.4 million customers, T-Mobile permits users to check voice mail without entering a passcode, as long as they're calling from their own phone -- an easy matter to fake with caller I.D. spoofing. http://www.securityfocus.com/news/9822
Hackers have discovered that the handy feature that tells you who's calling before you answer the phone is easily manipulated through weaknesses in Voice over IP (VoIP) programs and networks. They can make their phone calls appear to be from any number they want, and even pierce the veil of Caller I.D. blocking to unmask an anonymous phoner's unlisted number... Most subscribers have come to take Caller I.D. for granted, and some financial institutions even use Caller I.D. to authenticate customers over the phone.
To do this you only need the linux open source pbx software Asterisk
more about asterisk
Asterisk is a complete PBX in software. It runs on Linux and provides all of the features you would expect from a PBX and more. Asterisk does voice over IP in three protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware.Asterisk provides Voicemail services with Directory, Call Conferencing, Interactive Voice Response, Call Queuing. It has support for three-way calling, caller ID services, ADSI, SIP and H.323 (as both client and gateway). Check the Features section for a more complete list http://www.asterisk.org/