Because of its support for non-GSM SMS protocols, like UMTS, IS-95 (CDMA), CDMA2000, ANSI-136 (TDMA) and iDEN, the SMPP is the most commonly used protocol for short message exchange outside SS7 networks.
Depending on the volume of messages that are require to be pushed, means to connect to the SMSC could be different, such as using simple modems or connecting over leased line using low level communication protocols (like SMPP, UCP etc.) Advanced SMS banking solutions also cater to providing failover mechanisms and least-cost routing options.
The UDH is used in other protocols for short message transport - Short Message Peer-to-Peer (SMPP), Universal Computer Protocol (UCP) and in WEMT teleservice in CDMA2000.