After too many hours fighting with poor quality free wireless I am trying out mobile broadband. A friend loaned me his Sierra Wireless 597 3g. After installing the Snow Leopard drivers from Sprint it works fine.

However if I attempt to connect a pptp or ipsec vpn the connection drops with the error: “Disconnected. Multiple connections are not allowed. Your CDMA connection was terminated.” It behaves the same way if you attempt to connect to a wireless network.

The fix turns out to be simple. In SmartView:
Tools->Settings
click Hardware
select ‘Allow Simultaneous Connections.’

Here’s the link that got me on the right track:
http://forums.juniper.net/t5/SSL-VPN/Sprint-SmartView-disconnects-when-NC-launches/td-p/9579;jsessionid=C56E06204F45FFF85712812235447301