Should I buy an iPad with Cellular facility?

I sold my laptop yesterday. Now I need a replacement for it. I know an iPad can't be a replacement for a laptop. But I feel it can help till some extent. I'm not a movie freak. I just listen songs, browse internet, watch movies sometimes(twice in a week). And I work with .docx, .pdf, .pptx and .xlsx kind of files to finish my official stuff. Now I'm willing to buy an iPad, so... Question number 1 - Should I really buy an iPad? Is an iPad just another phone having big screen size? As I need a replacement for a laptop, will buying an iPad help with having value for money? If I should buy an iPad, then - Another Question - Which iPad should I buy? An iPad with cellular facility or just a simple one? What are the advantages of buying an iPad with cellular facility over non cellular facility iPad? What are the advantages of buying an iPad with no cellular facility over cellular facility iPad? I already have a phone which is quite good and it supports 3G cellular services also. Confused, please help!!!