planning to travel solo in the southern highlands?

A good place to start is Mendi, centrally located and easily accessible by plane. I wanted to go to Tari.
At the Kiburu lodge I met some friendly local business people who kindly advised me NOT to go there on my own as robberies along the road are common (they are). Their brother John could show me around and "escort" me as he knew a lot of places and is a streetwise guy. So he did, for the next three weeks across the southern highlands. Especially rewarding was the fact that I got to meet a lot of local people whom were keen to show me their land, villages, burial grounds, etc. We went to Lake Kutubu and around, to Mt Wilhelm, etc.
As John found it a great experience too, he would like to do more of that kind of guiding/escorting. You can contact him by email: johnonge@gmail.com (checked every week) or on his cell phone (digicel: 72 56 56 63, b-mobile: 636 80 57).
He is also planning to open a guesthouse soon in his village in the hills around Mendi (beautiful).

Thanks for the info. I've been thinking about visiting the area for some time.