Smallhagrid.
You mentioned the use of a answering machine.
I have several systems out there with just an answering machine. I even have one with 4 answering machines! It is a matter of what you can provide and at what cost the customer is willing to pay. When someones VM dies, and they are not heavy users, and they need some time to budget for a new system, this is a viable solution.
This job sounds like a Buddy job where payment will be parts + beer
So, to answer your question. The NVM is expensive to replace and is a bit tricky to program. Is it good, yes. Is it worth $ to repair, doubt it.
The i-series uses (I believe Carl pointed out) integration digits. These integration digits can be rather long with *****s and originating extensions and called extensions and forward/recall reasons,Line numbers and caller IDs. SO depending on what VM you get, you can customize what the VM does when it recieves these strings. A lot of these VMs even have built in digit grabbers or utilities that walk you through setting up your integration. The SOHO sounds like a perfect fit. but like I mentioed earlier, if all you want is a general mailbox, then an answering machine will work fine.
Also, keep in mind, we here try and do a "best practice". WOuld I put in a 124i as a "new" install, absolutely, I have plenty laying around that I can put together and feel rather confident having them run for years. I would also let the customer ( Usally a non-profit, or a buddy's house) that because this went in for free, don't expect it to last a week. Would I do this as a "business practice"? No. With someone's business, the fact that their business may depend on a phone call can dictate that the need for "newer" hardware. Keep in mind that suggestions are made with that thought in the forefront of our minds. We look at trying to look after a customer, foster a relationship, and ensure that the customer can keep the phones ringing.