If you're feeling needlessly complicated, you can even go from your phone's headphone jack to the X3's aux-input and then from the X3's aux-output to your car stereo's 3.5mm port with two cables. I'm not sure why you'd want to do that, but you have the option.
Of course, the optimal connection method uses your phone's Bluetooth connection to send calls and music. In this way, you gain both the ability to take control of your device to play, pause, and skip via the AVRCP controls on the X3's face and to make hands-free calls via the device's pinhole microphone.
The hands-free calling system is a simple one: there's no address book sync or built-in voice command system. However, the system will pass your spoken commands through to your phone's voice command system after holding the blue call button for a few seconds -- not a bad feature to have if you're already a fan of iOS' Siri or Google Voice Search.
Interestingly, I had a slightly harder time finding a clear station with the FlexSmart X3 in my San Francisco and Oakland testing areas than I did with the GoGroove SmartMini, which I assumed to be largely identical internally. I've got a few guesses as to why.
Firstly, the way that automatic scanning for a clear FM station is initiated by pressing and holding the "play" button on the X3's face. However, touching the X3 caused my hand to act as a sort of external antenna, artificially altering the transmitter's performance and creating false positives for clear stations. It would show all clear, until I removed my hand from the device and then the signal would fade again. It wasn't the end of the world, I just had to make sure not to let my fingers linger when channel scanning to guarantee the best results.
Automatic tuning is made all the more difficult by the fact that, like the SmartMini, the FlexSmart X3 is able to tune even as well as odd decimal frequencies (88.4, 88.5, 88.6), whereas most American car stereos that I've encountered can only tune to odd increments (88.5, 88.7, 88.9). This means that about half of the stations the Smartmini returned were frequencies like 104.4FM that my car couldn't match. Sometimes tapping a manual tuning button one tick up or down one decimal place would help, but usually I just had to try autotuning again.
Finding a clear station may take a bit of care and work, but the FlexSmart X3 is definitely capable and up to the task -- which is saying a lot. I was able to find serviceably clear signals even amid the crowded air waves of downtown San Francisco. When the signal got hairy, sometimes just a tweak of the FlexSmart's neck was enough to restore clarity. Other times, a new station was just a few taps away. Once I got outside of the metro areas and onto the open road, I was able to quickly lock in on and hold clean channels with little effort at all.
Audio quality was merely OK, but that's par for the course when you're talking about FM transmission. Anyone who claims "crystal clear" clarity from an FM transmitter is either exaggerating or has a tin ear. On our test car, a 2006 Chevrolet Aveo, I noticed that X3's FM transmitted audio was characterized by a high-pitched alternator whine that rose and fell with the engine's revs. This minor annoyance wasn't evident when testing GoGroove's SmartMini in the same vehicle or with other radio station on the FM band.
The GoGroove FlexSmart X3 performed well, but at the end of my testing, I recommend GoGroove's own SmartMini BT for those drivers for whom FM transmission is the only option for car audio. Both devices are about the same price; both give the user a variety of ways to connect their high-tech phone and even the most basic of car stereos; and both are operated with similar levels ease.
However, the SmartMini BT was just a hair more consistent when scanning for and hanging onto those quiet places among the crowded airwaves than the long-necked X3. Additionally, the high-pitched alternator whine that annoyed me with the newer FlexSmart X3 wasn't present with the more compact SmartMini device. My guess that the darker SmartMini presents a lower-profile target to would-be thieves is just the icing on the cake.