There is a known issue with this, and Skype is working to resolve it
Yes they fixed it allright! - reply from my support request on this subject:
"As of July 22nd 2009, it is no longer possible to assign online numbers to your Business Control Panel for regular consumer members. New online numbers purchased after July 22nd can only be assigned to business owned accounts created over the Business Control Panel. Business accounts can be created here:
https://secure.skype.com/business/manage/addusers under ?Create a business account?."
To say that I am unhappy is an understatement. Only days before this, I created skype names, invested in skype specific hardware, and purchased online numbers through the business account control panel, and purchased 100 euros of credit. Plus we planned an overseas marketing campeign based on the new number, and our exisitng skype names.
Now I find that because Skype have created a new class of user to fix this, I cannot use assign the online numbers to the skype names we have. Of course, the skype names have value, as they are know by our contacts, so we can't just change them, and as we all know, skype names don't just go away.
I guess this is all OK, since skype gave me a 2 euro voucher!