Cellular modules may or may not come with a SIM slot.  A SIM is required.

The Digi Connect WAN GPRS is available now for $450 MSRP. For more informat=
ion, please visit http://www.digi.com/products/cellulargateways/. For more =
information about Drop-in Networking, please visit http://www.digi.com/prod=
ucts/wirelessdropinnetworking/.

http://www.sparkfun.com/products/9270   $80

http://www.sparkfun.com/products/9533   $60
You can use this module to accomplish almost anything a normal cell phone c=
an - SMS text messages, GSM/GPRS, TCP/IP, and more!
There is no SIM socket on the actual cell module, you might want to conside=
r using our SIM card breakout board.

http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=3D47152  $1=
34

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