I recently tried to setup my Nokia N8 phone with a new StraightTalk SIM card that I purchased here: http://straighttalksim.com/
It was kind of a pain in the ass, so i figured i would save some people the trouble and walk them through the process.
First, activate the SIM online following the instructions in the package. No phone needed.
Once the SIM is in the Nokia, the 2 things to do are setup Mobile Web and MMS messaging.
1. In the Menu, select Settings > Connectivity > Settings > Network destinations > Access point
2. Automatically search for available access points and select Mobile data. Name it whatever you want ("StraightTalk" seemed reasonable) and add it to the "Internet" destination.
3. Once the new access point is created, click on it to edit the settings. Select options from the bottom right menu and then Advanced Settings.
4. Select "Proxy server address" and enter: proxy.mnvo.tracfone.com
5. For port, use: 80
Make sure you set this access point as the highest priority. You can go ahead and delete the ones from your old carrier. At this point, you should be good to access the internet from your phone.
Next let's set up MMS.
1. Go back to Settings > Connectivity > Settings > Network destinations and choose "New destination" from the bottom right menu. Name it: Multimedia Messaging
2. Add a new access point, automatically search, select Mobile data, and name this one (again, can be anything but "StraightTalkMMS" seemed reasonable).
3. Go into the access point and for Homepage enter: http://mmsc.cingular.com
4. Then under advanced settings, enter: 126.96.36.199 and 80 for the Proxy address and the port respectively.
5. Finally, back in the menu, open the Messaging app and select Settings from the bottom right menu. Under "Multimedia Message", select the new MMS access point you created in steps above for the "Access point in use" option.
Now you should be all set up to send MMS and mobile data. Enjoy that cheapo no contract phone service!