Analogue or Digital?
Wired or not?

Do you mean ringing tone; ie, what the calling party hears in their earpiece, or the ringing signal; ie, the signal on the called line which causes the bell to ring?

To put it another way, are you dialling or answering?

You should try a 'Search' of this forum, as phone interfaces are quite often discussed.
In particular, you should review this Thread - regarding the Legal & Regulatory issues which may be involved in connecting anything to the Public telephone system in your territory:
http://www.8052.com/forum/read.phtml?id=25529&top=