Final answer:
Osteoblasts are the cells responsible for secreting osteoid and initiating calcification during intramembranous ossification, and they eventually become osteocytes, the mature bone cells.
Step-by-step explanation:
The cells that contribute to the process of calcification during intramembranous ossification are primarily osteoblasts.
These bone-forming cells secrete osteoid, the uncalcified organic part of the bone matrix, which includes collagen fibers. Within a few days, the osteoid calcifies as mineral salts are deposited onto it.
As this process occurs, osteoblasts become entrapped within the bone matrix and ultimately differentiate into osteocytes, which are the mature bone cells responsible for maintaining the bone's mineral and organic matrix.