How do the words "blackberry" and "text" exemplify the evolution of language?
Languages change in three major ways. They experience changes in vocabulary, pronunciation, and syntax. The two words that you mention here are examples of one way that vocabulary change can occur.
One cause of vocabulary change is changing technology. Sometimes, words have to be made up for new technology. The words "telephone" and "television" are examples of this. At other times, words that already exist come to have new meanings. This is the case with your two words. In both cases, these are words with established meanings. At this point, they still retain their old meanings but have come to have new ones as well. This can happen randomly (as when the firm decided to call its device a Blackberry) or it can happen as an old idea is applied to new circumstances. (It is logical to differentiate between a voice message and a text message. It is also logical and common for a noun to become a verb in the way that "text" has.)
In these ways, the words you have selected are good examples of how languages change over time.