Can I have APNs for two networks?

[Guest Broc]

I have some PAYG Orange credit to use up but I want to test a tmobile sim on the phone - can I simply enter tbmobile APNs either manually or as an apk (assuming there is one) and not wipe the Orange APNs?

Newbie :P

[Guest Broc]

Sorry, I know it's a boring question but I don't want to screw up my phone.