Question : Client Changed ISP, now Blackberry email does not work

Good Morning Experts...

One of my clients changed their ISP from ATT to Cox Cable ( DSL to Cable )... and after fighting with the owners of the public DNS to change the MX records, none of their blackberry email works... Is this something the Client needs to contact their phone company (ATT) For?

Answer : Client Changed ISP, now Blackberry email does not work

How were they connecting to their email, BIS or BES?