I had posted this in response to a question in the domain newbies section:
As an investor in NNNNN.com's and operator of nnnnndomains, a blog devoted to these domains, welcome to the world of numerics!
These 5-digit .com's were all bought out in February, there are 100k total. Nearly half are already developed sites, most of these are US zip code sites owned by Marchex, which also owns the .net version of these zip codes. Good US zip codes will sell for $2k+ (often to Marchex) and smaller population zip code areas will sell for decent amounts as well. The next biggest use of NNNNN.com's is as Chinese sites, I think about 8-10% of NNNNN.com's are Chinese sites, and three of the top 100 Chinese sites are NNNNN.com's. In China, numerics are very popular as numbers have a lot of cultural meaning and are easier to remember than english letters.
After that, there are various uses of NNNNN.com's as mobile phone related sites, either for 5-digit mobile phone numbers or for words spelled on cell phones (like 74992.com spells Pizza.com on a phone keypad and is owned by WordDial.com, a company that is developing sites for mobile phone searching, or 62623.com for OANBD, Open All Night Business Directory). Other uses for NNNNN.com's are related to product numbers, such as 10015.com used by Adequate.org for the ISO 10015 quality assurance standard, and 10061.com used by Timberland for a popular boot number. Type any 5-digit number into google shopping and you will see a lot of potential uses for that number.
NNNNN.com's also can be used for foreign postal code sites, similar to Marchex's US zip code sites. Kuwait, Brazil, France, Germany, Sweden, Italy, Mexico, and other countries all use 5-digit postal codes. Finally, some NNNNN.com's are just use as nice short brandable domains for a website, 78746.com is related to Belize vacations, 48073.com is a contemporary art site. Go figure!
Anyways, the market for numerics looks very good now, 173.com sold for over $300k recently, and the values of NNN.com's (around $12k minimum) and NNNN.com's (around $500 minimum) have been rising recently. NNNNN.com currently go for around $10-$20 for non-premium numbers, and much higher for US zip codes or nice repeating digits. NNNNN.com's also have the advantage that they get traffic, some get a little and others get a ton (I earn >$5/day on some of my NNNNN.com's). So, given that they are all bought out prices should steadily rise if history is any guide. If mobile phone websites that are words spelled in numbers start to take off in popularity, that could significantly increase the value of NNNNN.com's that spell words, and probably push up the whole numeric market as well. If google ever gets around to promoting its site 466453.com (spells "google") for mobile phone users, or some similar event occurs, this could really take off. It takes a lot less finger taps on a cell phone to type in 466453.com (or any word-number) than spelling out the whole word.
The other main sources of growth for the NNNNN.com market will probably be the Chinese market and the foreign postal code market. Internet use is rapidly growing in China, I think internet penetration is currently only around 15% of the population there, and there are a LOT of people in China! Since numerics are so popular there, this bodes well for future values of these domains. Also, foreign postal code .com's have yet to fully take off, but there are rumblings here as well. Proxiti, a French company, has bought a lot of the NNNNN.info domains that represent French postal codes, so we may see more interest in this segment of the market as well. In short, there are a lot of areas for future growth in this market, as mobile phone searching, the Chinese market, and international uses in general are hot areas for internet growth.
I could go on and on about these domains, I really love my NNNNN.com's
Anyways, check out the blog to read up more about NNNNN.com's, and let me know if you have any more questions.