PlusNet (**768) peer not working

Hi,
I have a friend on PlusNet, he was the one who recommended you to me. He has a PlusNet SIP number but I am unable to call it from my Softphone.
Every time I try to call his number (**768xxxxxx) I get the message "407: Proxy Authentication Required"
I get the same message when trying to contact the PlusNet echo test. (**7687000)

I understand that I have to wait 3 days from registration to make oubound calls, but my 0844 number works fine, so at least he can call me.