From what I understand, it's fairly expensive. It's tough to make a profit on a phone when the battery costs $500. Costs are surely coming down but I think we'll have to wait before it hits the mass markets. From the wikipedia page on graphene [1]: "On the other hand, the price of epitaxial graphene on SiC is dominated by the substrate price, which is approximately $100/cm2 as of 2009."
[1] http://en.wikipedia.org/wiki/Graphene#Occurrence_and_product...