Drive a 4.8V servo signal line using 3.3V

It will probably work with 3.3V as a PWM signal level as long as VCC is at the rated 4.8V. The Vcc label, as opposed to Vdd, suggests TTL level logic where logic high is 2V to Vcc. Just try it with a 3.3V PWM and see what happens. The important thing is to have the servo and microcontroller GND references connected.

Edit: You can also use a nMOS or npn BJT using an inverting configuration. Connect the gate/base to the MCU PWM pin, the source/emitter to ground. The drain/collector is the output and must also be connected to V+ through a resistor. When the transistor is on, the output is pulled to ground. When the transistor is off, the output is at V+, minus the voltage drop across the resistor. Since this is a control signal and the current small, that voltage drop will be insignificant.

Note that in order to use a pMOS to avoid the inversion, you would have to pull its gate to V+ to stop current flow. However, since your PWM from the MCU is only 3.3V you won't be able to do that. You are thus limited to using a n-channel MOSFET.

Depending on what microcontroller you're using for PWM they often have the ability to set the output pin as open drain so you can take you PWM signal and have it set as any voltage you want