Dex One and Yahoo have extended and expanded their long-term partnership to roughly double the geographic coverage of the existing distribution partnership. The arrangement essentially involves business profile pages sold by Dex being served up in Yahoo Local search results, now in all 28 states where Dex One operates. The original partnership, formed in 2007, covered only the 14 western states that made up the old Quest Dex operating territory.

In today’s announcement of the deal expansion, the two companies say the success of the initial agreement led to the decision to expand it across all of Dex One territory. What isn’t clear is why this decision has taken three years.

Dex and R.H. Donnelley merged in 2005, forming a publishing company covering 28 states. RHD was renamed Dex One early this year following its emergence from bankruptcy protection.