As I am spending this Holiday season in Brazil, you can only imagine that I did some research in the area of prepaid sim cards with unlimited data. The best thing I came up with was Tim Brasil. They sell prepaid cards for R$ 10 (around US$ 5), and you can buy additional credits in grocery stores by increments of R$ 6. Data connections are charged R$ 0.50 per day for unlimited usage, though speed is capped if you use more than 10 Mb in 24 hours or 300 Mb in 30 days. Voice call prices are kind of hard to understand but basically if you call another Tim number or make a local call to a landline, you will be charged R$ 0.25 per call no matter how long you stay on the line. Calls to other carriers are more expensive and charged by the minute (R$ 1.39 per minute if I got that right).
Using a jailbroken iPhone with MyWi works with the aforementioned plan and there are no APN settings to tweak. Since Tim won't sell microsim cards under that plan, you'd better bring a sim card cutter along if you plan on using an unsimlocked iPhone 4.
You may also want to check the sim card you're buying as some don't allow 3G connectivity. Only Tim owned stores seem to be selling those. Resellers don't (and unfortunately I could not find a Tim owned store where I am located)!
It is a no brainer for me as the 300 Mb that I'm probably gonna use in the next 2 weeks will end up costing me less than R$ 25 (= US$ 12) with some phone calls and text messages included in that price. If you compare this to an estimated charge of € 4000 (€ 13/Mb) by Orange France for the same usage, it looks like the best deal ever!
Please also note that you'll need a CPF number to buy a sim card (so you might ask a Brazilian friend to go to the store with you)!
If you have questions, feel free to leave a comment and I'll be happy to help.
