I'd really try hard to just move them to a hosted exchange. In the long run, they will be far happier and it will work far better and offer them far superior reliability, features & performance.
I'm a big fan of PayPerCloud.com and you really can't beat the price - around $8/user/month. Exchange doesn't have to break the bank & it certainly doesn't mean a huge investment in hardware & software.
Sell them on the features & benefits like:
- All emails, folders, contacts & calendars will sync to ALL your devices; everyone has a work PC, iPad, iPhone/android, home PC. Inevitably people want to access all their info from each of those devices, or more than one.
- Backups; PSTs are harder to backup & manage backup of multiple workstations; with a hosted exchange, they don't have to worry about that any longer.
- Overall superior reliability & performance. I get virtually zero calls from my clients who either host their own exchange & we maintain, or use PPC. My POP/IMAP clients on the other hand....ugh...it's a mess.
One other thing to consider is I had one client that thought they also wanted to have ONE shared office calendar; it quickly became clear it was a big mess. Nobody knows who put what event on the calendar, it's not clear who is supposed to attend, managing info & details is a big pain. They very quickly had us delete the single shared calendar and instead give read access to everyone's calendars (and in some cases read/write) so that everyone could see everyone else's.
Trying to do the "one shared office calendar" doesn't work too well, IMO.