Service instability with iPhone 3

[ojtinkerbell]

I recently migrated to an iPhone 3 and am having ongoing issues with the network connection dropping out. Its worst when I try to use maps, but can drop the signal during texts or calls as well. It happens indoors, outdoors, city and rural.

I've tried switching off wifi and resetting network settings but the problem persists.

Any ideas?

***Edited to add labels***

[FidoStephane]

Hi there ojtinkerbell, 

It sounds to me like you are using an old 2G SIM card. You can get a new SIM in store for only 10$. If the issue is indeed with your SIM, this will resolve your issue. 

Let us know,