i was look at an older phone just because they were cheaper like the 8700g but i was not sure if i could use it because my alltel phone does not have a sim card and i was not sure about the hole unlocking thing either any ideas
Alltell is a cdma network the 8700g is a gsm network. Mainly unlocking phones is for gsm networks. Jewertt is correct the 8830 world edition and 8330 curve are sold by them. You should also be able to get an 8703e or a 7250 if you want an older device for cheap. They both will work on alltell.
Also, you need to make sure that if you are purchasing a used BlackBerry, it needs to come from AllTel. ESNs are registered with each CDMA carrier. You will have a very hard time trying to get a phone from another carrier (Verizon, Sprint) to be registered with AllTel.