We have this issue where someone calls, it can be inbound or outbound, and the receiver just hears ringing. Sometimes it seems if you put the caller on hold and then pick it back up it will work, other times it wont. We have a ip900 with ESI 60 gigbit phones.

Has anyone seen this issue before?

We are kind of stumped.

Yes. If you have SIP trunks on the system it's a known issue according to ESI. The work around according to ESI is to move them from SIP trunks to a PRI or similar handoff. I ended up installing an ADTRAN to convert SIP to PRI handoff and ESI gave me a PRI card to put in the system.

If you're not on SIP trunks check to make sure you're on the latest software version.

We are using ESI SIP trunks.

So ESI said it was a known issue with SIP trunks?

I think we are a little behind on firmware also.