Hi thanks for the answer, but I think I said some things the wrong way.
a) the phone is called optiset 300 advance
b) the phone does not have the posibility to resolve names (like xyz.dyndns.org)
c) it does not support SIP
I need a service “in the internet” where my phone can register itself, so that i would be available throug a E.164 number. I found some free public SIP services, but i did not find any without SIP working with my phone. I would be glad if somone knows such a public (noncommercial) server.