For direct competitors to voip.ms you have Call Centric or Anveo. These providers have comparable levels of features where you can basically create a cloud based phone system with 95% of the features you might expect on a full PBX just minus a few little things (Paging, BLF button support, and phone provisioning are the ones I can think of). Anveo (not anveo direct) has impressive features to build customized call rules but it can be a bit of a learning curve at first. Call Centric is also popular, I have no personal experience here.
On the full service side you have your Ring Central, or 8x8 type of providers. These tend to be pretty expensive options, I don’t find them very interesting personally but I can see the appeal for some. If you just want a business phone system with full features but don’t want to run any of it yourself these are good.
On the Trunking side you have your Flowroute, Telnyx, Twilio, and dozens of others. A mixture of capabilities often exist where they claim to be more than simple dumb trunking providers which is fine. Twilio and to lesser extent Telnyx for example is heavy into exposing API control so they tend to integrate with a million third parties. I personally really like Telnyx here. Usually do not have IVR, or very limited IVR features and few if any more enhancements that let you build a PBX type functionality. Maybe only voicemail for these kinds of providers.
Next you have the wholesale aggregators. Bare bones SIP trunking services that focus on least cost routing at the cheapest rates possible. This would be Anveo Direct (Not anveo retail) and ThinQ. Maybe not always the best choice and they can be hard to setup as you pretty much need a PBX and likely static IP with fairly permissive RTP ranges on the firewall. I love using these as the outbound carrier for calls from internal PBX. The prices are so crazy low it’s amazing to me how a average SMB company can basically use 10k outgoing minutes a month for what is lunch money. Price is around $0.002/min (2/10th of a penny a minute)
BulkVS is one that seems to be somewhere between wholesale aggregator and trunking provider. They were more focused on providing e911 service early on, but have moved quickly to add more full slate of services. Now they are the cheapest option for inbound trunking in many areas by far, the 911 service they provide is still very good and valuable, outbound they are a weak option (fill in the weak spot with anveo direct if you need more than basic north american calling). I’m finding these guys a very interesting niche player that fills in some important holes for me.
Last is the true wholesale providers like Bandwidth, Iristel, and other CLEC providers and if you have the scale for it direct connections to some big tier 1 carriers. Can be harder to work with, might require minimums or longer time to sign up and be approved.
So for the purposes of what to do while you wait for voip.ms to mitigate the ddos? Likely depends on how you are setup. If you have lots of individual phones trying to register to voip.ms server it can be hard to go back and reconfigure everything. Anything you change temporarily probably needs to change back eventually. Service is working a bit better though still intermittent. Might want to setup forwards to mobile numbers while you wait.
If you have a single PBX and you can add a new SIP trunk and change a few routing rules it will be easier to put in work arounds. With another carrier your outbound calling should already be solved. Inbound calls, maybe forward to temporary number? Forwarding seems to have worked ok for me today so that seems like something they worked to fix. Will be harder for them to fix SIP traffic to customer phones while ddos still ongoing, at the end of the day when they hammer you with traffic there isn’t much you can do with it except try to get the upstream flows blocked but it’s whack a mole.
As things go longer, those ddos nodes can start to burn out too (isp abuse reports, customer “fixes” their broken routers, etc)