Generally, each base station within range receives all messages from your phone. Even if you were to address different messages (with different response delays) to each station, they would all still "see" the other messages. They then record that message (or an identifier - akin to a TCP sequence number) and compare the (synchronised) time at which this message was received. This is used to calculate the difference (thus delay) of each tower's reception of that message.

I don't think what you're suggesting would actually work given the way mobile network infrastructure works (where multiple cell base stations may see each message at the same time).