Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
simple connect RXD of the arduino to the RXD of the GSM 900 and the TXD to the TXD of the thing.
if there is a level converter, like max 232 on the module, use a level converter (max 232) with the arduino too.. if it works in TTL logic, its okay.