No one likes receiving SPAM. Getting a sly email about cheap pharmaceuticals is not great, but receiving a text message from a company you don't have any business with is a pain... it's invasive and a waste of time.
A recent case saw McDonald's warned over sending emails to people who had not requested them, as part of a 'send to a friend' campaign. In addition, there was no 'unsubscribe' facility for users to opt-out. Whilst they were not fined in this specific example, Coca Cola were not so lucky back in 2009 over a SMS message campaign which failed to identify Coca Cola as the sender, in addition to not providing a unsubscribe facility. Coke's agencies copped over $100,000 in fines from ACMA for this little mistake.