You have to do this through a wireless provider through a device called a GSM modem. The software to connect to the modem can be very complex to set up, and you have the pay monthly fees to the provider like you would for any regular phone plan, except you pay them for the ability to use the GSM modem to send out text messages.
There is an existing software called SMScaster but I keep hearing how buggy it is. What you are saying may very well exist but you are thinking of something too high brow for my needs.
So lets walk through this
1) There are several local cell phone providers that offer "unlimited" texting for a flat monthly fee on prepaid phones right?
2) These prepaid phones require no identification to get the phone. My friend got a phone in the name of Obama Fuck so now when he calls people it shows "Fuck Obama" on their caller Id. Hence using a prepaid phone would theoretically be untraceable.
3) There is open source software readily available like bitpim to upload contacts into a phone right?
4) Most phones are no manufactured to send a text to everyone in the contacts list right?
So what we need is a version of bitpim that will feed chunks of a .csv file of contacts into a phone send a stored text message to all those contacts erase the first set of contacts rinse and repeat.
You could get crazy with this and have the software controlling 10 phones at once.. you would only be limited by how many USB ports you can come up with right? So 10 prepaid phones blowing out 400 texts a minute 24 hours a day for a month. 4,000 texts a minute times 43,200 minutes in a month right? That is theoretically 172,280,000 texts
You could blast a text to every phone in your areacode..