Proper SIP URI?

[engineercarl]

I have been doing a good deal of searching both here and in the DSLR forums regarding the proper format for a SIP URI for my DID. I have seen the following examples:

XXXYYYZZZZ@apollo.voipwelcome.com
XXXYYYZZZZ@sip.voipwelcome.com
XXXYYYZZZZ@in.voipwelcome.com
XXXYYYZZZZ@in01.voipwelcome.com

Which one is correct?

Carl

[VOIPoTim]

XXXYYYZZZZ@in.voipwelcome.com