The frequencies are not the same in every country and also the cadence of the tone bursts is not the same in every country.

You can find helpful information on this problem by searching with Google using a search key of telephone call progress tones. Also note there was a chip made many years ago by a company called Signetics. The number for the chip was the NE5900. This chip and its corresponding applications information could be useful to you in learning more about call progress detection. Later sold by Philips, an NE5900 application note is still available here or from Philips USA here. I am not actually suggesting that you have to use the NE5900 chip......the App Note just has some good information. The part has been discontinued anyway and is only available in the residual inventory marketplace.

Michael Karas