66601 will get forwarded to
yourfriend@voipstunt.com, as long as you use yourfriend as replacement, do not add @voipstunt.com.
Another thing: add your voipstunt account to the VSP list and select this account in the provider section of the dial plan.
so:
priority= nbr
pattern= _66601
replacement= yourfriend
provider= your voipstunt account