You may find this article useful in configuring your phone.
Sometimes there are minor differences of how to configure from one VoIP provider to another. So, it may be helpful to know who your VoIP provider is that you are configuring it with.
For example, CallCentric requires the additional configuration of Auth ID as well as UserName. But, your VSP appears to not use that info for registration (some providers require this; some don't). In the case of CallCentric, Domain, Alt Domain, and Outbound Proxy would all use the same entry; i.e. callcentric.com. In this case, no IP address is required, just the domain/proxy names (IP addresses are looked-up using DNS lookup). So, again it just depends on your VSP as to whether they accept domain/proxy names, or an explicit IP address. Also, Callcentric requires the setting "Use DNS SRV" be set to "YES". But, not many VSP's require this setting. So, this may not apply to your VSP settings. (they would specify, if required).
If you still have problems, more detailed information about your VSP, your LAN, and your Router may be needed.