Nearly all full-time Ph.D. students receive financial support. Typically, a student is admitted with a Teaching Assistantship and a tuition waiver. Students who help with summer teaching can earn additional money. A student involved with a research project will often change to a Research Assistantship. Research assistantships usually pay more, and they are for 12 instead of 9 months.
Some fellowships are also available for both entering and more senior graduate students.
Fellowship pay can be significantly greater than teaching or research assistantship pay.