I'd prefer to work off actual numbers because I use them myself.
Brand name key words are leased for $500/month
Generic key words are leased for $10k/month nationally or $250/month on average by telephone code
This is the Yellow Pages model: company rents keyword (pretty much forever) and revenue base is stable.
The last numbers PR had 1,000 brand keywords leased, plus another 9,000 by the end of April (April 4, 2010 PR).
Assuming these are all national numbers:
$500 * 10,000 = $5,000,000/month * 12 months = $60,000,000/year
Total outstanding shares: 1,407,023,309
$60,000,000 / 1,407,023,309 = $0.043 per share revenue
Fair multiple for revenue: 15x (cheap growth stock)
$0.043 * 15 = $0.64 price per share
This is an asbolute base calculation using only the numbers we have now. It doesn't assume the $0.04/min as of January 1, 2011; future growth in revenues in the US; any international expansion.
The number may be smaller because We don't know the composition of the voice keywords.
I think the presentation above is a fair guess.