Although some players considered it nothing more than phoning a friend who then calls another person and puts the two phones together as a short cut around the regulation, it is strictly against the PokerStars Terms of Service:
“Real money play is not allowed from within the US under any circumstances. Players who attempt to play for real money from inside the US with the aid of VPNs or other technical workarounds will lose their playing privileges and/or funds in their account.”
Until recently, many US players had gone undetected, but now reports of accounts being suspended and funds frozen are starting to spread.The weak point in using the VPN connections is when the inadvertently disconnect, they temporarily reveal their true source, which PokerStars has become more sophisticated and noticing and logging. Apparently, it is when players ask for a cash out that the extra scrutiny is brought to their account to verify their true location and playing history.