Celluar technology has advanced since the days when the "bag phone" was
common. Digital phones and infrastructure (e.g. base station) equipment
can receive & process signals at a much lower signal strength than
analog phones. Besides, the weakest link is usually the receiver in the
phone, not the phone's ability to transmit to the base.

If you do a lot of travel to locations that have less than ideal cell
coverage, I would consider a handset that can be connected to a car kit
with an externally mounted antenna. This will help the receiver in
situations where you are in an area with weak coverage. Also, some
providers such as Sprint PCS allow you to add, for a fixed monthly fee,
analog roaming service to your dual-band handset for off network
roaming.    

Hope it helps.