For me I think Mike's already mentioned it, get a telesales lady in and hammer the database, that also cleans your database too.
You could start with a mailshot or email and follow that up. That's how we do things, mail or email first then telesales follow those up. The conversion rate on a followed up mailing is far above the cold call rate, as the telesales isn't a sales call, its a "Hi this is Sam from XYZ the carpet cleaners, Allan sent you a letter with a special offer a couple of weeks ago and we just wanted to make sure you got that." SHUT UP and wait for response. Then Say "Was there anything you'd considered having done on the offer?" SHUT UP! Always remember the person who speaks first after the close 'loses'.
You can pay someone to work from home part time to do telesales, we used to use a customer who was on maternity leave from her full time job. OR you could get an Apprentice in to run things for you, cheap as chips, and keen as mustard most of them, the benefit is they can do some of your other admin and telephone answering too.
Al.