Phases 1 and 2 were defined before 3G networks existed, and as such support adding IN services to a GSM network, although they are equally applicable to 2.5G and 3G networks.
阶段1和2是在3G网络出现之前定义的，因此它支持将IN（智能网）服务加入到一个GSM网络——尽管这些服务对于2.5G和3G网络来说也是同样可用的。