Serine/threonine protein phosphatase that may dephosphorylate and activate lipins. Lipins are phosphatidate phosphatases that catalyze the conversion of phosphatidic acid to diacylglycerol and control the metabolism of fatty acids at different levels. May indirectly modulate the lipid composition of nuclear and/or endoplasmic reticulum membranes and be required for proper nuclear membrane morphology and/or dynamics. May also indirectly regulate the production of lipid droplets and triacylglycerol. Induces neuronal differentiation by antagonizing BMP signaling. Acts both by dephosphorylating BMPR1A and by promoting BMPR2 proteasomal degradation (By similarity). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Interacts with bmpr1a, bmpr1b and bmpr2. Belongs to the dullard family.