iMessage came out when most cell phone plans had expensive SMS/MMS rates. Your basic plans used to get 200 texts per month. After that you would be charged $0.05/text. I didn’t have a text plan on my personal phone at all until they became unlimited.

When the original iPhone came out Blackberry dominated the business users. They had blackberry messages or BBM. Many of the things you associate with iMessages were copied from BBM.

The only reason that iMessages took off in the U.S. is because unlimited texts was part of the required data plan. Outside of the U.S. the cell phone companies continued to charge for texts. iMessage that would sometimes send it over SMS/MMS and sometimes over the data plan was stupid. So the other messaging platforms became the norm.