It isn't possible to transfer numbers from one line to another within AT&T's system.
Your options are basically:
A. Swallow the ETF on the 3GS's line.
B. Move the two lines into a family plan, drop all features from the 3GS line and suspend service on it so it only pays $9.99 a month until the contract ends.
Odds are that A will be the cheaper option.
Your options are basically:
A. Swallow the ETF on the 3GS's line.
B. Move the two lines into a family plan, drop all features from the 3GS line and suspend service on it so it only pays $9.99 a month until the contract ends.
Odds are that A will be the cheaper option.