1) That`s right, activate and use the E-71 as long as you wish. If you ever have trouble with the Iphone, put the SIM back in the E-71. Move the SIM to any other phone and back, a different phone every day.
2) The same SIM goes in either Nokia. Since you must keep the E-71, most people choose it over the other. WIFI is the important difference.
Sorry, mixed up on which phone to be purchased used. Your OK with a used iphone.
Refill on-line with the SIM in any phone, no need to move it back to the E-71. Although if you had to contact a CSR they might ask for Info off the E-71 that wasn`t really necessary they ask.