I have an unlocked iPhone5 that uses a T-Mobile micro-SIM. I'd like to use that iPhone in China with a Chinese SIM, and use an old Blackberry Bold for emergency calls to/from the US on T-Mobile. Unfortunately the Blackberry uses a mini-SIM, and I'm apprehensive about damage if I use one of the mini-to-micro adapters to insert the iPhone's T-Mobile micro-SIM into the BB.

What would be ideal is to have an active T-Mobile mini-SIM for use in the BB Bold while I replace the T-Mobile micro-SIM in the iPhone with a Chinese SIM while in China. The T-Mobile micro-SIM would be retained for entry to the US.

Does anyone know whether T-Mobile will allow two active SIM cards with the same phone number? I would never be using the different T-Mobile-enabled phones with the same number at the same time.

Sorry, they don't do duplicate sims. But an adapter won't cause any damage, I swap sims around all the time with no issues.

T-Mobile (or any GSM operator) will not allow two active SIMs at the same time. If you have an active device and a second device with the same SIM information is on line at the same time the account will be deactivated to prevent fraud.

Another thing you could do to keep your main and a different account (such as a local prepaid account) is to use a forwarding service on your primary number with a service such as Kall8 so you could receive calls that were directed to your main number to the prepaid.

Any suggestions for a source? I've heard people having damage and needing to use their fingernails to fix tiny bent prongs. I don't want to destroy my full-price iPhone that way!

Your iPhone won't get any damage because it is using the original nano SIM - the Bold is using a normal (mini) size sim, and because it has a "normal" slide in slot, damage risk is very minimal.

I use this set:

http://www.amazon.com/gp/product/B00...ag=prd_idnr-20

Just make sure the sim is in flush and you'll be fine.

Many overseas providers when suppllying their nano sim cards, as a courtesy also provide adapter for regular sim card slot.....they know folks often swap back and forth. At least in Asia