If you are confident it's for cellular, it's a single band 3db 800 mhz and it only has lmited value at this point. An ideal external antenna is dual band 800/1900 for north american backcountry use and would have two coils on the mast. (by the way, antennas don't care if you are digital or analogue)
Based on the value of replacement antennas (about $30 - 50), I would only keep it under one condition. That's if your current cellphone has an external antenna port and you can buy an adapter for it to connect to the antenna. 90% of new phones sold do not have antenna ports anymore so if you are a blackberry or iphone user, that antenna has no value.
Based on where you are using it, that antenna could actually reduce your coverage. If the area is covered with 1900 mhz, you are not going to pick it up with that external hooked up and your internal antenna may not pick it up well with that one hooked up. If it's covered with 800 mhz, you will see big gains. Fortunatley providers like Verizon cover a large amount of rural in 800 mhz.
If you see a booster or amp in your future and you are thinking of keeping that antenna for it, don't. The new antenna technology would be worth the upgrade.
Pete