Aside from that, there really isn’t a huge amount of difference between a mobile phone and a walkie-talkie. Just like a walkie-talkie, once you talk into the speaker, your voice is converted to an electrical impulse and relayed, via electrons housed inside a small antenna, to the intended recipient. Then, just like with a walkie-talkie, those same electrical impulses are converted (via a reversal of the initial process) back into your voice. Mobiles, like walkie-talkies, have small, compact aerials and use relatively small amounts of power.
However, unlike walkie-talkies, mobile phones can communicate with one another over much vaster distances. How? Well, this is the REALLY clever bit. The cellular network divides up land into cells and each cell has its own phone mast. The phone mast boosts the phone’s signal, in essentially the same way a signal tower does for a radio network, except that they relay the signal from your phone to other cell towers, allowing the signal to carry across much further distances without significant degradation.
Of course, there are only so many available radio frequencies in any given area. Walkie-talkie users prevent the mass chaos that uncontrolled broadcasting/transmitting would no doubt cause by licensing and heavily policing radio usage (in fact, we covered this exact subject earlier in the month).
Imagine if emergency services were unable to use their radio frequencies! Awful. It is therefore very important that frequencies in use are policed and this is why you cannot buy radios with a power output stronger than 0.5 watts without a license.
However, mobile phones operate differently. Each mobile essentially re-uses its own frequency, in a similar way to a licensed radio frequency might. It is rare that all possible frequencies are in use at the same time, but it actually does happen (think: New Year’s Eve).
The majority of the information in this article (basically, the bits we had to look up and/or double check) was sourced from this article on Physics.org.