The Arduino boards are typically 5v devices, and have either an FTDI FT232 usb-to-serial IC, or a ATMega16u2 usb microcontroller with usb-to-serial code.
To connect the serial pins 0 and 1 to a separate device, you either need to remove the Arduino's main microcontroller, or make sure it does not try to access the serial pins (a blank sketch would do).
To connect them to a 3.3v device, you would need a level shifter. The Fonera will not tolerate 5v on its serial pins.
The MSP430 Valueline Launchpad runs at 3.6v, as does the IC providing the serial connection. 3.6v is close enough to the 3.3v Fonera levels that it should be okay. Most ICs can accept VCC + 0.3v on any given input pin. No guarantees though.
As a note, the Fonera requires 9600 baud. The Launchpad UART is limited to 9600 baud, hardcoded, so it will work with the Fonera, but not with some newer devices that need a faster serial speed.