Iphone 3g slow with simcard inserted

[Mesopotamian5]

Hello! My sincerest apologies of this is a subject that's already been discussed, but I have looked around without succes for a while now.

Thing is, I tried to jailbreak this old iphone I have lying about, and it took forever (I'm not that jailbreak savvy), but I finally got it working.
It runs beautifully as an ipod, and everything works fine - Until I stick a sim card in it. What happens is beyond my understanding. It slows down to a truly unusable speed. It is literally 5-10 seconds about reacting to anything I do. Swiping between pages on the home screen, opening apps. It's all 5-10 seconds things, if not longer.
Any input? How come it runs perfectly(Faster than my un-broken iphone 4) without the simcard, but with the simcard it's unusable? What'd I do wrong? Is it hardware?

Best wishes from a hopeful noob.

 

[iDonev]

Let's rule out the telephony stuff - insert the SIM card, turn Airplane Mode on and try using the device. Is it still laggy?

 

[Mesopotamian5]

Yes, still lags on airplane mode. It took a good 15 minutes to make through the laggy menues, but it still lags on airplane mode. I suspect it must be a hardware issue. The Simcard must be putting pressure on the processor or something.

 

[iDonev]

I use a 3GS on iOS 6. While it does lag a bit due to old hardware, it's nothing like the lag you describe. It is worth doing a backup and restoring the phone as new. Test to see if that speeds things up.

Update: Before restoring see if Resetting the Network Settings on your current setup has any effect.