The media gateway that you were talking about is the media gateway/softswitch that carry the bearer? isn't the MSS/MSC is the controller of the media gateways using the H.248/MEGACO protocol?
It reduces burden in the MSC by moving the switching capabilities to the MGw. The overall solution (Sofswitch) has a lot of benefits. I'm specialized in this area; let me know if you need more details.
The first supplier (vendor) in the market is Ericsson when it comes to market share and technology leadership.
Then comes NSN (Nokia Siemens Networks) in second place then Huawei from China in third place as per 2009-Q4 reports.
Softswitch Solution is available in Fixed (Wireline) Networks and is known as Telephony Softswitch Solution (TSS). It is also available, of course, in Mobile Networks and is known as Mobile Softswitch Solution (MSS).
To know more about MSS, I recommend this white paper from Ericsson about "Efficient Softswitching" that can be found here: