Possible to make Touch Tone Phone Ring with no phone line?
A telephone ringer is driven by a high AC voltage oscillating around 30 times per second (70V RMS, 30 Hz). This can vary, up or down, slower or faster. It's not particularly picky.

Below is a simple Ring Generator circuit, using a transformer wired "backwards", driven by a dual 555 timer (556 IC). It expects 12V 400mA, but again, can use more or less. I suspect You could even power this from a few (6?) AA batteries in series if you didn't want to use a wall wart.




  This ring generator will ring a telephone once every 10 seconds. The interval between rings can be lengthened or shortened by varying the value of the 1 Meg resistor. The 70 volt/ 30 Hz ring voltage is produced from the 120 volt side of a small 12.6 VAC power transformer (Radio Shack 273-1365). Both capacitors connected across the transformer windings are non-polarized / 100 volts. Circuit draws about 300mA from the 12 volt DC power supply during the ringing interval. 


A relay or switch at the +12V node should be used to turn the circuit on.

See Wiring up old phone ringer to arduino or http://www.bowdenshobbycircuits.info/page11.htm#ring2.gif or  https://www.sparkfun.com/tutorials/50 for some more ideas.