SimCash is the physical premium currency in The Sims Social. It is the way that EA are making money from the game. As such, there is no way to get SimCash for free, unless directly from EA. Any links, surveys, registrations etc. claiming to give your Free SimCash are bogus, and could result in malware, viruses or people using your personal details for their own gain. Play The Sims Social with plenty of friends, listen to the people that you trust, and do not believe what you read on the Internet (anywhere else!). Bear in mind that the game is run as a business and anything that could detract from that is going to be vigorously policed.
EA have the power to give out SimCash, and they have done to some people for the number of problems with the game so far. Some Sims have been completely reset and their owners compensated with large SimCash rewards (2500 SimCash!), while others have received just 150 SimCash for the issues. Unofficial sources, however, simply cannot give you free money!
You also should get 20 SimCash when starting the game. Some users have not, but EA are adamant that they will get it eventually. See this link for confirmation: http://help.social.ea.com/app/answers/detail/a_id/5568/~/how-do-i-get-my-20-free-simcash?