Sim cards are available in all countries in the region for a few dollars, or for free when you put some initial credit on the card. Notable exception here is Turkey. Don’t get a Turkish sim card if you are traveling. It stops working after 10 days on a foreign phone (only a phone bought in Turkey will work, or registering will cost >100$) and the initial cost is more than 20$. Uzbekistan and Iran do not allow foreigners to register sim cards, so you need a local friend to do it for you.
Local sim cards or roaming?
So should you get local sim cards when traveling, or roaming? If you do not need mobile internet and just need to send some text messages, you can use your international sim. Otherwise, get local sim cards. It’s a small hassle for a big gain. The problem is that the local operators often don’t have roaming agreements with the neighboring countries, even if the same company operates there. Make sure you pass on your sim card to other travelers when you exit the country.
If you need to call internationally, you can get an international sim card. We don’t have experience with any of these; if you have, please let us know which one is good. Try GoSim, WorldSim or OneSim. UCallWeConn is a much, much cheaper alternative to Skype to call landlines or mobile phones when you are online.
Internet accessibility ranges from great to non-existent depending on the region; see the country pages linked below for more details. Important to keep in mind is that all governments in the region are enemies of the internet to a greater or lesser degree. Internet is filtered. You are being watched and unwanted websites are blocked. Social networks are sometimes blocked. Good proxies and VPN’s on the Silk Road are Psiphon and HotSpotShield (other recommendations are welcome).