Could you explain more specifically: What application you try to run on 7210 emulator? Have you tried any other emulators with the same application?
The "OutOfMemory" is thrown because the run time memory or heap memory has been used up. Try to use the Runtime.freeMemory() and Runtime.totalMemory() to check the momery use in the application, put them into certain place where you suspect can cause the "OutOfMemory" be thrown. You can also check the memory use from the status windows of 7210 emulator.
Different model have different maximum heap memory and there are many reasons can cause the "OutOfMemory" be thrown like loading the same picture for several time but not set the the used reference to null.
The 7210 emulator is one series 40 device emulator. There are quite lots of series 40 Nokia phones such as 7210, 6610, 6800, 6100, 5100. The concept emulator can only simulate the MIDlet running on series 40 phones. The device emulator is supposed to be exactly same as the device and based on the device software, in another word if the device has a bug then the emulator has the same bug.