Well, if that's your business plan, it seems like its nothing more than an extension of domains... which provides no benefit to the customer. Why spend money on a "keyphrase" when you can spend money on the actual domain?
I don't see what possible reason a person would have to pay for a keyphrase? Most people use sites like tinyurl to send links to friends, why would I pay for a service like that? If I was a company, I would just buy a domain with that keyphrase (e.g. www.keyphrase.com) or do something like companyname.com/keyphrase
I think a better monetization plan would be to load the long url link in an iframe and put ads on the top of the page.