I realize this is an old thread, but I wanted to chime in.
My company manages the entire data collection process for a wind energy developer.
We started using the AMPS iPacks as soon as they were released, and struggled a LOT in the beginning. Additionally, we experienced changes by the carriers causing problems (had one situation where it would NOT work for 3-6 months, but would work a mile up the road, but then would start working as mysteriously as it started). NRG has been as helpful as they could in working through those issues, but there's only so much that can be done. The carriers tend not to care about data.
We also tested some GSM iPacks. While the reliability of them seems to be much better than AMPS, setup was still a bit of a headache (just getting AT&T to call back).
So.. We've not standardized on satellite iPacks. I was udderly AMAZED at how easily these units deployed. I converted 13 units in a very short amount of time and other than a few human-created problems (typos), things went off without a hitch. The MItchMail service is reliable and has been a good middle-man when we've experienced in-house infrastructure changes that caused problems with delivery. Lastly, it's very rare to have any transmission problems now. My client is in the northeastern US, so winters can get cold and getting to the sites becomes impractical. We had "zero" trips this winter due to iPack failures. Historically, we'd have a couple for one reason or another.
If you can afford the higher monthly costs and the cost of the equipment, you'll more than save that in hassle.
George Friend President Prodigium, LLC firstname.lastname@example.org