Adafruit Slim Sticker-type GSM/Cellular Quad-Band Antenna - 3dBi uFL [ADA1991];

That's one slim cellular antenna! At just 75mm long from tip to tip and and with a thickness of just 2mm, this 3dBi GSM antenna is slim, compact and sensitive, with a 3dBi gain.  The antenna juts out from its base with stick-on back so you attach it to an enclosure if you're making something like, say, a DIY phone.  It has a tiny uFL connector on the end - which is perfect for the  FONA - but will also work well for any other RF project on the 850/900/1800/1900/2100 bands, such as any other Cellular or GSM/GPRS device.

We also offer a version of this antenna with a longer 300mm cable .