Have a look at this headline in a newspaper:
It took me several minutes - and the help of my wife - to understand this headline.
Why?
You may not see any problem with it. But I kept interpreting the noun pay as the object of the verb block, resulting in an imperative: block pay. I then interpreted as you go phones as a subordinate clause, but immediately stumbled as it doesn't make any sense. The way the headline is laid out doesn't help, nor does the fact that no hyphenation was used.
What is being blocked are pay-as-you-go phones.
This kind of construction is called a garden path sentence, because when you start interpreting such a sentence you are being 'led up the garden path'.
The most famous example of a garden path is this one:
The horse raced past the barn fell.
Initially you interpret the sentence to mean that the horse 'raced past the barn', i.e. a structure in which we have a Subject (the horse), then an intransitive verb (raced) and then an Adverbial in the shape of a prepositional phrase (past the barn). But then you get to fell, and the sentence no longer makes sense.
You've been led up the garden path!
So how should the sentence be interpreted?
Well, the intended meaning is for raced past the barn to be a relative clause, as in:
The horse that was raced past the barn fell.
In this sentence the grammatical structure is different. The Subject is now the horse (that was) raced past the barn, and this noun phrase is followed by the intransitive verb fell.
Want some more examples?
The old man the boat.
The complex houses married and single soldiers and their families.
Time flies like an arrow; fruit flies like a banana.
Head over to Wikipedia for an explanation.