While that is true, I do remember looking at a Nationwide GSM map provided by VoiceStream, and NONE of the GSM systems that one could roam on at the time were adjacent to each other. All were very distant from each other, in major metropolitan areas (and a couple of second-tier locations where PCS spectrum was cheap back in the day). So, unless you made a call in El Paso, Texas on the VoiceStream network, and then instantaneously transported to, say, New York City on the Omnipoint network, there was no chance you were going to be able to test intercarrier handoffs. As such, I would bet real money that no intercarrier call handoffs were set up between the GSM carriers back in '96 ... it just wasn't physically possible to do until much alter, when the networks expanded.
Now, AMPS providers there were plenty of in '96. Some did do roaming handoffs, and some didn't. It all depended on how amicable the relationship was between the neighboring cellular companies.
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