thanks guys for your helpful replies
now it is partially solved but now what's happening:
i installed the sip setting on fring for nymgo and then it works great!
so i thought i had a problem with n900 sip
so i tried different company like TPAD a without fring and it works very well
i can manage myself now by using fring but it's a bit hard to use fring when u have your own sip system in your phone which gives u much more options.
maybe NYMGO cannot be installed except on fring i guess!

anyway thanks for your help guys