For quite a while I had been able to use my Samsung Galaxy Apollo phone as a modem - I just plugged it into my work laptop (running Windows XP) and it appeared as a modem, which I could use to connect to the internet nicely.
Then I tried (and failed) to update my phone using Samsung Kies and it stopped working. I remembered as part of trying to get Kies to work I found an obscure code to type on the keypad to switch the phone between 'PDA' mode and 'Modem' mode. I have just managed to switch it back to modem mode, and this has got my modem working again!
To do this I had to type *#7284# on the phone dialer keypad. This brought up a menu where I selected the USB option to be 'Modem'
Now plugging it into my computer shows it up as a Samsung Mobile Modem. I have the phone number set to *99***1#, which seems to work ok.
I disabled the internal modem in the laptop because sometimes windows tried to dial that one instead, which is not connected to anything.