New update coming soon. This time a major one - I decided to switch to ethernet rather than a bluetooth communication. There are a couple of reasons for that...
First of all, I found a cheap ethernet module (ENC28j60) that's roughly $6 a piece and a good library for it (not the standard one) - that's more less as cheap as the cheapest bluetooth modules.
Secondly, it eliminates the need to have a separate android device to serve as a relay between arduinos and the internet - that gets annoying when you want to have a remote temperature sensor at home.
What's more, I think it will be easier to understand and troubleshoot than bluetooth communication since everything is more transparent (some ppl just couldn't understand that it's good to see what's being sent).
Finally, it allows to use all the different devices to access arduino (not just android devices, but computers and apple/ windows phone devices as well.... though that's through a browser not an app created with MIT's app inventor, but it's nice to have that option)
Not sure if I post it here or in a separate thread - probably in a seperate one because I am afraid it will get confusing after a couple of pages and ppl might fail to notice that there are completely two different methods.