While the original made its way to the DreamCast, GameCube, PlayStation 2, PC, Game Boy Advance (which... you can watch us play here at NGR....), as well as a few other consoles; the sequels never received such treatment. Crazy Taxi 2 was released on the DC, but wasn't seen again until the PSP collection which included both it and the original. As for Crazy Taxi 3, most people tend to forget it even existed. It featured one new map with new characters to play as, but it itself was more of a collection than a new game. It included an expanded map for Crazy Taxi and Crazy Taxi 2, with Crazy Taxi 1's city taking the spotlight. Thanks to the new jump ability it made the classic Crazy Taxi we all knew and love feel fresh, but it really wasn't anything new. (Although, unlike 2, it did receive an arcade release.)
So, where did the series go from there? It didn't. Port after port soon followed, and aside from cameos in other SEGA games, the series dropped off the grid. Until now that is.

Rather than having a free driving experience, this time around your taxi is always moving forward, and you control it by swiping left or right to change lanes. Tapping on the left or right side of the touch screen will cause you to drift and turn, but you are limited on where you can or cannot drive. Even when you drift, you are always locked into whatever lane you are currently in. This set up, isn't really a bad thing though.
If you are a long time fan, you have to realize this game is not Crazy Taxi 4. It is a mobile game based on quick reflexes (with you dodging traffic), and trying to figure out the best route to get a customer where they want to go. An arrow points you in the right direction just like before, but customers are actually picked up from a world map, where you tap on their icon to start their "mission" (or stage). The main focus of this game really is to dodge traffic, pick up coins, and smash things to score as high of a score as possible, but the game does at least retain the Crazy Taxi spirit. On top of that, you can easily add the original Crazy Taxi soundtrack in, so that's always a plus. (Just doesn't feel the same without All I want, and Way Down the Line playing.)
Although this Crazy Taxi is not what you can consider a main title, it is at least fun in its own way. The game is currently free on iOS, with an Android version coming out in the near future. There are starter packs you can buy (which allow you to unlock new taxis to drive, as well as upgrade your current one faster), but you do not have to spend a single dime if you don't want to.
On the other hand, if you want a real Crazy Taxi experience on your mobile device, then why not just download the original? Like I said earlier, it's been released on almost everything! (And the mobile version has the original soundtrack to boot! Just... No brand name stores...)