I have Virgin Mobile in the US (it's one of the cheapest options with good quality phones), and it seems the same. It made me set a 6-digit PIN as my password, and my phone number is my username. Here are the requirements listed on their website:

Your Account PIN must be:

-6 numbers (no letters or special characters)

-no more than 3 identical numbers in a row (222)

-no more than 3 sequential numbers (such as 234)

If I did the math right, that's approximately 900,000 possible passwords, which is obviously really low