To the contrary, I know a local company that deployed an IBM iSeries (previously AS/400) mainframe in their main office, serving two other locations connected via a metropolitan-area T1 line.
Just a small nit to pick. The iSeries product line is mini computers, not mainframe; that would fall under the zSeries brand.
The machine itself was pretty expensive, yet covered by a 5 or 10 year (can't remember) warranty. The machine would actually call a support technician out to the site whenever it detected an issue with itself, and this has kept their uptime at an astonishing rate, aided by a decent UPS and the hot-swappable hardware.
Parts of this also exist in their pSeries (Unix-class) product line. If I experience a serious adapter error in a management-console-connected server, a call will be dispatched to IBM. It won't be as fast as for their iSeries or zSeries products (or their enterprise-class storage systems, such as the DS8300), but it'll typically result in an under-24-hours resolution time (manually dispatched, however).
Oh, and our local Solaris admins freak out when they discover that, even on our older hardware (some of which is older than five years), I can do things such as replace a failed fiber channel adapter online, without our end users even noticing that I've done anything.
But this is the support I've come to associate IBM with, can't speak for their phone support although everyone seems to outsource to India for phone support these days (a problem I have frequently with Cisco).
Not sure about IBM US, but whenever you call for Canadian support, it most definitely routes through one of a few Canadian call centres (typically Markham, Ontario, if you're in the Greater Toronto Area; calls also get routed to support personnel in BC and Montreal).