Best approach to activate SIM from new 4S on a 4, and use the 4's SIM in the 4S

[forgotten247]

I tried to search for this but didn't find anything, I was wondering if anyone was in this situation and had a working approach or suggestions:

• I have an iPhone 4 and have been using it as my primary phone (this is my personal # I've had for a while)
• I am getting a new iPhone 4S with it's own SIM (new number, new account, ... this is as a work phone)
• I want to use my personal SIM in the 4S as my main device, and put the new (work #) SIM in the 4

I'm debating if I should activate the new SIM in the 4S first, and once it is working just switch the SIMs, or if there is a better approach, like putting the new old SIM into the 4S before doing anything with the new SIM, ...

Any thoughts/suggestions?

Thanks!