The Apple iPhone is generally locked to the phone company selling them. You cannot swap SIM cards.
Yes, as long as you have a SIM Card to swap in to avoid roaming charges.
To change the sim card on your iPhone simply open it at the back remove the battery and replace your sim card.
Seeing as how the iPhone 4 requires a micro-SIM you will have to either get a new micro-SIM from Vodafone; cut your SIM down to a micro-SIM; or purchase a dual SIM adapter that will allow you to use your full size SIM in it. I have included Related Links for the last two options as they include pictures that you may need to be able to make an informed decision as to which route you want to take.
Yes, as long as you swap out the SIM Card or put it on airplane mode so you avoid roaming charges.
The only way - would be to swap SIM cards. However - that would need the flip phone to be able to accept the iPhone's SIM card.
Yes, if you get your SIM card cut to fit into an iPhone 5c, it should still work in your Samsung Galaxy as long as both devices are compatible with the same network and the SIM card is active. Just ensure that the SIM cutting process is done correctly to avoid any damage. However, it's always a good idea to check with your carrier for any specific compatibility issues.
Of course, the iPhone 3G and/or the original iPhone will take any normal sim card; the 3G iPhone will take the 3G sim as well.
The Samsung Galaxy S4 accepts a micro-SIM, but not a nano-SIM.
Yes, you can share your SIM card between two separate Samsung devices, like the Galaxy S3 and Galaxy Note, but not simultaneously. You would need to physically swap the SIM card between the two phones each time you want to use it in a different device. Alternatively, consider using a dual SIM phone or a mobile hotspot if you need connectivity on both devices simultaneously.
In some situations, the status bar on your iPhone might display No SIM, even though your iPhone has a SIM card.
If you are with Sprint, there is no SIM card for the Samsung Conquer. Sprint does not use SIM cards.