This post is outdated, please visit;
We have been always looking for free SIP account providers and we have listed them quite a few times. Recently after visiting some of those listed, we have found that some of those accounts are not operating any more. Below are some that work and we will continue to test and list them here so you will be able to create SIP accounts free and fulfill your SIP communication needs. Following is not a complete exhaustive list but we will update it as seen fit.
(Ooops, I forgot my first ever Free SIP Account provider, IPTEL)
IPTEL.ORG. the original SER Creators
http://sip2sip.info A project by AG Projects, If you know OpenSIPS you know them.
AntiSIP, One my favorite and oldest SIP service providers, they were on the original free SIP accounts lists
PBXes or also known as i-p-tel GmbH, provides both free and paid services. (An expired security certificate seem to give trouble in accessing the server)
A Service from SIPphone, Does Gizmo project sounds a bell?
A community effort by VoIPUser, I think it is a fine service.
Disclaimer, me and my partners have service from all the above companies but we are not in any affiliated to them than using the free service.