Yes, it is possible to build a cell phone that can perform the functions of making calls, sending SMS, and even data transfer. For an example of a GSM module th

Yes, it is possible to build a cell phone that can perform the functions of making calls, sending SMS, and even data transfer. For an example of a GSM module that would be the main component of such a system, see here: http://www.sparkfun.com/products/10138 http://www.sparkfun.com/products/10138 However, from a cost and performance point of view, it doesn't make any sense to do so. The cell phone OEMs have a large amount of engineering and logistics resources to put behind building devices that are aesthetically pleasing, small, and powerful.