One of the key issues with the microspeakers used with smartphones and laptop computers is that their resonant frequency (known as F0) is up in the KHz range. Any frequencies below this frequency is going to be severely attenuated, and worse, extra energy that you pour into those frequencies (say, boosting them) is going to be converted directly into heat, with little benefit.
There's a nice definition of F0 in this document:
http://www.panasonic.net/id/ctlg/data/pdf/AID0000/AID0000PE3.pdfIf your lucky, some of the speakers you'll be dealing with will be like these ones:
http://www.cui.com/product/resource/cds-15118b.pdfHowever, I'm sure in the real world, they are much worse. (F0 on that one was 600Hz on a good day). Look at the frequency response curve -- you'll be 20dB down below 600Hz. Also look at hte distortion performance in that datasheet -- everything 1K and higher has pretty low distortion. Anything below 1K - garbage.
In addition, the dynamic range available in these loudspeakers is typically garbage (I hear rumours that some of them are in the 10dB range at some frequencies...). That paired with poor sensitivity (movement per volt) means that you have to drive these darns things very close to their physical limits to get any decent SPL.
Okay... so what does this mean for your mixes?
A lot of "vibe" comes from the drums and the bass. Your issue here is that most of your bass frequencies have disappeared below F0. Your snare and hats will stell get through quite well. You may be able to use harmonic enhancement plugins to add harmonics to your bass instruments. (like Waves MaxxBass). That'll create harmonics further up in the spectrum that can convince some listeners that they are hearing the bass guitar.
You're also very limited in dynamic range. You may need a little more compression, or possibly some limiting on your snare just to allow other instruments to get their say in the output.
A decent laptop/smartphone manufacturer is going to high pass filter some of that content before it hits the amplifier. Don't fight it. just move your content elsewhere. (i..e harmonic enhancement).
That's all i have for now. let me chew some more,I may post again.