While you can check Ooma's number availability here: http://www3.ooma.com/phone_numbers.php, I've recently found that some phone number exchanges were listed for the wrong city in Ooma's database.
You can check the correct information here: http://www.telcodata.us/telcodata/telco. You can also check all available exchanges by just entering the area code.
So, you may want to enter multiple area code/exchanges to find available exchanges in the area that might be incorrectly classified. You may be able to find a local number from Ooma that you wouldn't have otherwise.
If you're in an AT&T serviced area, you can use this site: http://localcalling.sbc.com/LCA/lca_input.jsp to determine local area codes/exchanges.