Uhh, not quite
Mobiles output the minimum amount of RF required to communicate with the mast, so if there are less masts then your average distance to a mast is going to increase - your handset will output more RF and your battery will need charging more frequently.
Now you need to figure out what the total extra power use is on the handset side, deduct from the network side savings and decide if it's worth the effort.
Good way to move the cost of power from the provider to the consumer though.