Want to hook up a voice synthesizer to telephone

[Thurston]

Hi new member here, sorry to dive right in without many posts but I wondered if someone could help me with the following question as I am not an electronics buff!

I have one of these; http://www.bossus.com/gear/productdetai ... ductId=414

Funniest thing ever, you can view it in action here; http://www.youtube.com/watch?v=jJRLWV7DIEk

I believe BOSS have discontinued the item now, but I managed to find an old one on eBay.

I want to hook it up to a telephone so that I can do prank calls on my mates, but I know nothing about electronics. Are there any companies or individuals out there who do bespoke electronics projects? I did purchase a unit off eBay that connects the BOSS VT-1 unit to a telephone, but there is a loud buzzing/feedback on the line. I want to hire somebody to get something set up for me.

Any advice?