Any NAT system will cause issues for certain VPN clients, as each client varies in its ability to deal with NAT. (Note that what’s actually taking place is PAT, not NAT, but since most users don’t understand thedifference, I’ll continue to refer to PAT as NAT.).
GENERALLY, almost any relatively modern VPN client program will work with a properly setup Antamedia server, using a protocol called NAT-T. We see dozens of Cisco VPN clients and PPTP clients every day connect successfully from behind our Antamedia server. I use a Sonicwall VPN client myself without any problems.
Where VPN clients generally fail to connect is when a network administrator has put an Antamedia server BEHIND ANOTHER NAT DEVICE. Almost no IPSEC VPN client can connect in this scenario. The common term for this is “Cascaded NAT” and it’s a problem.
When I travel and try to use a VPN client, I’m successful about 75% of the time. When the VPN won’t connect, so far it’s always been due to cascaded NAT.
If your Antamedia server is connected directly to the internet (not behind a NAT router), most VPN clients will be able to connect. If you put your Antamedia server behind another NAT router, you’re asking for problems and almost no IPSEC VPN client will be able to connect. (PPTP VPN will still work in most cases.)
There are other hotspot gateways on the market that support UPNP and/or have IPSEC pass-through support and therefore support a wider range of VPN clients. These gateways cost many times what Antamedia Hotspot does. The decision on whether to upgrade to one of these more expensive systems is yours. No system will ever offer everything to everyone.
For what it’s worth, our hotspots average 100,000 user connection minutes each day and transfer about 75GB / day. I have not had a single user complain about VPN connection problems in the last 2 years.