After you push home button on iPhone how do you summon Siri?

After you push home button on iPhone how do you summon Siri?

You rub the phone three times.

Put candles around a pentagram drawn with sand. Then arrange the bones of your first born within the pentagram. Then chant the following:

Sweet Mother, sweet Mother;
send your child unto me,
for the sins of the unworthy must be baptized in blood and fear

after the final line, ask the question or say the command you have for siri.

Hold down the home button until it comes up. Siri isn't on iPhone 4 or 3 though.