Unfortunately, if you now try to use the old methods of kinternet, wvdial or Umtsmon, you will find out that dialup will work with these, but you won't get a working resolv.conv and thus no name resolution. The reason is that the netconfig tools, which do rewrite resolv.conf apparently refuse to do that if NETWORKMANAGER=yes is configured in /etc/sysconfig/network/config.
One solution would be to switch to the old ifup method (NETWORKMANAGER=no), but then wireless LAN will basically be unusable.
Another, dirty and hackish solution is this:
Create a /etc/ppp/ip-up.local, containing
echo "nameserver $DNS1
nameserver $DNS2" >> /etc/resolv.conf
and a /etc/ppp/ip-down.local, containing
mv /etc/resolv.conf.netconfig /etc/resolv.conf
Make both of them executable. Dial up.
How does it work? The ip-up script gets the DNS servers in its environment. Just before it exits, it calls the ip-up.local script which then appends them to resolv.conf. During ip-down, the netconfig tools notice that the resolv.conf was changed externally and they refuse to touch it. They instead create resolv.conf.netconfig. ip-down.local now just replaces resolv.conv with resolv.conf.netconfig and everybody should be fine again.
To make this hack a bit more robust, you should probably check if the $DNS variables are non-empty before adding them and you should check if resolv.conf.netconfig is newer than resolv.conf before restoring, but I leave that up to the reader.
Oh - and don't forget to file a bug against NetworkManager if it cannot handle your device!