Given that parameter, everyone of us should ditch every cellular provider
we use and switch to a satellite phone!

Realistically, coverage, while important, is still only one of the
factors to consider.
In my case, value was far more important than ubiquitous coverage.  I use
T-Mobile- arguably the carrier with the worst coverage nationwide.
However, it works virtually everywhere I live, work and play, and costs
me easily $40 less than Cingular and $60 or more less than Verizon per
month (I have a two-line family plan with unlimited data on both lines
for $72/month plus tax.  Plus, ironically, neither Verizon nor Cingular
work reliably in the Denver suburb I live in, but Sprint, T-Mo and Nextel
all do!)

The closest I could come to matching T-Mo's price was a Sprint SERO plan,
but it would've required me to shell out over $400 for phones and
activation fees (we both use Windows Mobile phones, so I'd have needed a
6700 and a Q to replace our MDA and Dash) but in return we'd have better
coverage (and faster data.)

In the last two years I've only been one place without any T-Mobile (or
roaming) coverage (Grand Lake, CO), that had coverage with other
carriers. (I've been in a few places, however, mostly National parks,
where no carriers had service, at least according to my trusty ancient
Nokia 5120 TDMA/analog handheld with manual A/B system selection I
carried for emergencies)

And, I've certainly been in many places with lackluster/spotty coverage
on T-Mo where other people seemed to have no trouble using their phones.

However, given that mankind has spent 99.999999% of his existence without
cellphones, I hardly think having coverage in every single hotel room or
tourist trap I vacation in is worth that much more a month to me.  I used
to use Beyond Wireless TDMA/analog prepaid service (on the aforementioned
Nokia 5120) to fill in the gaps in T-Mo coverage, but since T-Mo added
850MHz roaming, I found I only used a couple of minutes on Beyond in all
of 2006.  Maybe, if I find myself without T-Mo coverage again soon I'll
add a Page Plus (CDMA) phone to the repertoire but suspect I'll manage
fine without one!

!Amen, amigo!  That's EXACTLY what it's all about !
---Juan

If coverage was everyone's priority then Verizon would have 95% market
share.

In fact, there are other priorities that some people have. Some people
want a single phone that can roam in much of Europe and Asia, and are
willing to give up some U.S. coverage and use a GSM carrier. some people
are willing to give up coverage in return for a lower price. Some people
are willing to give up voice coverage in return for better data coverage
(which helps Sprint at the expense of Cingular).