I am inputting values into a spreadsheet using Apache POI. These values have newlines, and I was able to use this code successfully:
CellStyle style = cell.g
The only way I got this to work was write my own implementation to calculate the row height. The code is now released as the Taro project, so you could use that. It has numerous convenience methods to let you write an Excel file in far fewer lines of code.
If you prefer to put the implementation in your own code, you can find it in the SpreadsheetTab class. There is an autoSizeRow(int rowIndex) method half way down. It basically iterates down the row and for each cell finds the number of lines of text, then uses the font size to calculate the optimal cell height. It then sets the row height to the height of the tallest cell.