The 8880 is not intended to be attached directly to the PSTN. It resides between your microcontroller and a DAA (data access arrangement). The DAA is what attaches to the PSTN and provides so-called two-to-four-wire conversion, on/off hook control, (incoming) ring indication, and sometimes a means to control the off-hook impedance for pulse-dial pulse shaping (country specific). The PSTN side of the DAA is connected to TIP and RING. The other side of the DAA and is connected to the 8880's "audio" IN+, IN-, and TONE signals as well as the microcontroller pins that you designate for hookswitch control output and ring indicate input.

Have you checked the manufacturer's website for appnotes showing a typical application? Also try a Google search for "data access arrangement".