Phones.com has an alexa ranking of 637,000.
Using a fairly accurate chart I've contributed to at
http://www.sillyjokes.co.uk/alexa/index.php
that turns into about 50/day uniques, or 1500/month.
All of that has to be direct typein, which usually converts very well. If I put a decent affiliate program on there, (especially cell phones) I could probably make about $30/sale, which would come to about $16K/year just off the traffic and using a single aff pgm with an "average" CR.
If, on the other hand, a cell phone company used it, where they could get $ from recurring fees, that number would jump at least 10 fold. So phones.com is worth $32K to $320K depending on who buys it.
Knowing this, I can say phones.net is worth $3.2K to 32K, depending on who your buyer is.
disclaimers: yes, I know Alexa is not the best ranking system, as it distorts the highs & lows and tends to squish everyone in the middle. Yes, I know, the typeins for .net are less than 10% of .com's. But it's better than pulling the numbers out of thin air.