eMail is the still the way that most of my customers contact me. I believe in answering my eMails immediately. So when I go out during the day, I want to remain in contact.
In the past I would drag my laptop around with me when I went out. Except to boot up the PC and then connect to the Internet using a dongle takes time. So i got myself an Android Smart Phone and started to check my mail on that. Typing an email on a tiny keyboard tends to be awkward, so I got myself an Android Tablet and find it much easier to carry around with me and type on it.
Now I have a PC, a Tablet and a Smart Phone which I use in different circumstances to perform some business function. Which means, I need to synchronise the three machines. The easiest way and quickest way to do this is to have the same APP on all three.
Smart Phones Apps will be released as free or paid and may be only for one Smart Phone Platform or it may be released for more that one and often have a PC equivalent making syncing across the different platforms possible.