GSM gateways in the US?!?

[Network Fortius <netfortius () gmail com>]

$subj says it pretty much all :) Does anybody use anything like this  
in the US? The $1 mil/yr costs of our cellular telephony consists,  
almost exclusively, of calls made from cell phones, back into the  
company's various sites PBXs. I have seen such things advertised in  
Europe, with the extraordinary benefit of (by using a GSM gateway)  
making all calls appear "inside the GSM network", thus very low cost,  
or, sometimes, even free ...

TIA,
Stef