Here is a basic formula that will count carraige returns. If you need to actually count how many rows you are using, as in where the cell pops text on to the next line, that will depend on the width of the cell and gets kind of tricky.

local numberVar strLen := len({call_req.description});
local numberVar loopVar := 1;
local numberVar CRCount;

for loopVar := 1 to strLen do
(
  if mid({call_req.description}, loopVar, 1) = chr(10) then
  CRCount := CRCount + 1
);

CRCount