Hi Mat,
Well based on its Keyword Value and Market size I would have to place a guestimate of 8/12K but could be more, if a Major Phone retailer is looking to get some cheap free traffic this would make for a sound business investment. Its not easy to Value a Domain without detailed traffic and revenue details so my valuation is based on Instant Eye Appeal, take your anual revenue and and x4 or maybe x6 if your lucky, this seems to be the trend right now.