What is the typical prognosis for bone metastasis of breast cancer?

Poor. Metastatic breast cancer, like other disseminated cancers has poor prognosis. However quality of life can be improved through proper pain managment and hormonal/chemo/radiation therapy.
Treatable, NotCurable. The term "prognosis" is like an on/off switch and does not take into account disease control and quality of life. After all, diabetes is incurable but doesn't have the same connotation as cancer. Many breast ca patients with bony mets respond very well to rx and can live for years with this. It is best to focus on response to rx rather than cure.
Generally poor. However more women with stage IV bca are living longer with good quality of life thanks to advances in therapies.