What alternatives do I have for telephony if my LEC says the Central Office has an issue?
I'm not sure if you are asking for DR advice in your situation or a more permanent solution.
However, for DR, I would HIGHLY recommend Telecom Recovery
We use them and love their service.
Our local provider has failover (either automatic or we can force manual) to send our DID 100 blocks to multiple 888 numbers at Telecom Recovery that are tied into a software PBX that allows for automatated attendant, fax, conference calling, hunt groups, etc. You setup people's cell phones, home phones, remote office lines, etc. and then tell the software PBX where to route the calls.
So when local PRIs are down, we run off this DR system and customers/etc. can still reach us. Outbound calling is still limited to cell phones (or internal desk to desk on the existing PBX), but that's cool with us.
(NOTE: not trying to push product, they have just done a great job for us and this might help others)
How about cellphones and a bucketload of SIM cards?
OR. Depending on how dirty you want to get.. Have you got a fibre connection (dark, ideally) to the datacenter?
Get a pair of Optical Add/Drop multiplexers. Put one in the DC, put one in the Office. In the datacentre, have Verizon supply you with ISDN over fibre. Plug it into the OADM. In the office, you'll need to configure the other half of the mux pair to break that ISDN wavelength out back to an ISDN converter.
I had a quick google about, and there's a whole bunch of different brands of ISDN to ethernet converter, and ISDN to IP converter (or TDM to IP). There's even some that'll convert ISDN to MPLS frames, and back again.. So even though you're not doing VoIP (Although, frankly, this is probably the route i'd be going down), there's still options, so long as you can get a circuit into the datacentre (and you can get data service from there).
It appears (from more googling) that the magic keyword is "TDM over IP", or "Circuit Emulation". There's even some Cisco routers that can do it.. Apparently the 3660 Multiservice platform, with some specialist Network Modules.
Found another TDMoIP platform
Would you be looking for a workaround or a replacement for the faulty service?
Replacement: If you can get an additional data line put in, you reserve it for telephony and you can run VoIP across that. This can be a line out to a dedicated provider that deals with telephony themselves and you can get good quality from that. There are "hosted telephony" providers out there and VoIP doesn't have to mean "Skype on a bad day over a dial up" line quality.
Workaround: It's difficult to know what to suggest if you don't think the sort of VoIP providers that run across the standard Internet connection will cut it (though again, if you have the bandwidth and can configure decent QoS to a decent provider you might be surprised). Other than that, it's Longneck's suggestion.