I partially agree. For the hotline bit, it's desirable to have someone there full-time, but you could still say "our hotline can be reached at these and those times". Makes it a bit cumbersome for clients, but then again, it's a start...
And for the consulting/support contract stuff: I think everything is possible if you are upfront and honest about it. If you go ahead and tell your clients, "we will sell you support but we can only guarantee this and that response time", some might buy it, some might not - at least you have offered it.
It should not be uncommon in the open-source community that developers are struggling to make a living off their software and that they have to support it by having a day job.