You can consider the mobile M-Zone or the new power of Unicom's UP, but since most users are mobile and M-Zone sends messages outside the network, if your friends mainly use mobile, I suggest using M-Zone. If your friends mainly use Unicom, I suggest using UP new power, which is cheaper! If you usually send less messages, you can also use the mobile Shenzhouxing, because it has no monthly rent, and you can charge as much as you want, which means that SMS and phone bills are a bit expensive!