Sure thing… hopefully someone can benefit from my $150 mistake 
I do lots of surface mount stuff (using my SMT solder/hot-air rework station), but this wasn’t an option for the BGA GE863 footprint. So I picked up a hotplate from Walmart and did some experimenting with some other boards/components to get proficient.
When it came time to mount the GE863, I ran into several probs:
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Took a lot longer than it should… I suspect this is because the GE863 absorbs so much of the heat.
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Although it’s BGA, it’s more like Solder BGA… the balls are solder, not solid balls, and the heat was not even enough to melt all solder balls so the board would sink down. Perhaps it had a different melting point than the solder paste I was using.
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Very difficult to remove board from the hotplate without having the GE863 module slide around a bit. I probably should have taped it down better.
Eventually I had it placed, double checked for shorts, and powered up the module. I was able to send/receive AT commands, but:
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The unit seemed to reboot (silently) every 10-30 seconds, even with a solid power supply.
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The SIM interface wasn’t working 95% of the time. I got it go SIM READY a few times, but most of the time it reported SIM ERROR. I think it registered on the network once, although maybe that’s just my brain shedding a positive light on the experience
I suspect both of these were a result of overheating the module during reflow, since my prior rev of the circuit worked fine with the GM862. I wasn’t willing to blow another $150 to see if my 2nd attempt would be more successful.
In the end I had to respin the board again to meet some changing requirements, so I reverted back to the GM862.
IMHO, having the SIM holder on the expansion board makes a lot of sense, since it’s not an optional part of the system, and the Telit docs have some pretty clear/strict guidelines around the SIM holder.
Hope that helps!