A foreign communications service provider may be listed in the US (i.e. go public in the USA so as to have its equity securities trade on US financial markets, listed exchanges or otherwise) without necessarily having to be compliant with US federal regulations for telecommunications companies.

That said, Skype is a different story: as long as the company has a physical, operating unit in any given country with plant, equipment and corporate management personnel here, the company opens itself to the possibility of being regulated by the authorities having jurisdiction where such company assets and business activity is conducted reside.