The 3000 has both FXS and FXO ports. How do you have it connected to the 28i switch? (in other words, what kind of card is each wired to).
It's been my experience that the i-series switches do no properly generate CPC signals on analog station ports (4-ASTU cards). When the remote party disconnects, the switch is supposed to briefly disconnect battery on the POTS line to tell the CPE that the call has ended.
https://www.sandman.com/cpcbull.html The i-series instead goes right back to a dialtone, which causes endless problems for answering machines, fax machines, etc. (pretty much anything besides a simple telephone).
It's possible that a way to generate a proper CPC is burried somewhere down in the programming options, but I've never found it.
