Mobile phones nowadays are almost universally using microSD for the storage of additional data onto them instead of other formats that were used previously. Examples of these formats may include MMC, miniSD, Memory Stick Duo and M2.
Reduced power requirement
A chief advantage of microSD cards over other larger cards such as SD cards was that they consumed only a fraction of the power as other cards. This property did not particularly help in other applications such as in camcorders as they already had much larger batteries and power savings from microSD cards were not that noteworthy. However, in smartphones this power draw was a substantial portion of the load on the battery and microSD cards helped improve battery life significantly.
Along with reduced power requirement, microSD cards also were quite a lot portable than other competing standards such as SD cards. Although this portability did not have an effect on the weight of the devices, the devices using microSD cards could be made much more thinner and microSD cards did not get in the way of other components within the phone such as smartphone displays.
Although the size of SD cards is an advantage in cameras due to the easier handling requirement of them, this advantage is negated to quite an extent with smartphones. A reason for this is that camera memory cards are swapped much more often than in mobile phones and if they used microSDs, the chance of losing a card would increase greatly which is not that much of a concern in smartphones.
Becoming a de facto standard
MicroSDs became popular as most of the mobile phone manufacturers decided on using them in their phones. An exception to this rule was Sony Ericsson which was always bent on using Sony’s proprietary Memory Stick technology in its cellphones. It created the Memory Stick Micro (M2) card specifically for use in Sony Ericsson phones and was a direct alternative to microSD cards.
However, as the popularity of the MicroSD standard kept increasing, Sony Ericsson found its proprietary card equipped phones to be at a big disadvantage in regards to the competition and started adopting microSD cards in some of its phones, starting with the Sony Ericsson K850i in 2007. In mid-2009, Sony Ericsson announced that it had completely dropped support for M2 and that all of its future phones would support microSD.