DID number and Asterisk

[pw44]

Hia,
i do have a voipcheap trunk configured, and it works wel for outgoing calls.
To be able to receive calls, i got a DID from ipkall (www.ipkall.com), and have it defined to my voipcheap account (number: my voipcheap username and proxy: sip.voipcheap.com).
When a call to the number assigned to me, i get busy tone and my asterisk log shows:

Code: [Select]

messages.1:[2010-09-18 17:14:01] NOTICE[10678] chan_sip.c: Call from '2064246841' to extension 'voipcheap-user' rejected because extension not found.
As i understand, i need to assign an extension.
Is there someone using something like i'm trying to do that could help me with this issue?
BR,
Paulo

P.S. I'm also planning to get a second DID number and link it to the same voipcheap account. Is it possible? How?