Since its intial rollout in 1985 with three carriers using an analogue-based system, the cell phone industry has evolved and grown into a product and service that have become almost essential to out everyday lives. Now, 32+ years later we have multiple carriers offering various services marketed towards key consumer segments. There are a number of carriers that build and maintain physical networks; Bell, Rogers, Telus, Wind (and Shaw turning on spring 2011), although there are many brand names reselling services on those networks (Koodo, Solo, Fido, Virgin, PC Choice, 7-11, etc). Below is a chart outlining the technology breakdown of the carriers and their physical networks.

CARRIER
(in Alberta)
NETWORK
VOICE
Frequency Band
DATA
Frequency Band

HSPA1,5
850 & 1900 MHz
850 & 1900 MHz

LTE8
n/a
700 & 850 & 1900 & 1700/2100 MHz
 
Mike (iden)
800 MHz2
800 MHz2

HSPA1,5
850 & 1900 MHz
850 & 1900 MHz

LTE8
n/a
850 & 1900 & 1700/2100 MHz

GSM5 & HSPA5
850 & 1900 MHz
850 & 1900 MHz
LTE8
n/a
700 & 850 & 1900 & 1700/2100 & 2600 MHz

AWS
1700/2100 MHz
1700/2100 MHz

AWS
1700/2100 MHz 1700/2100 MHz
1 this is a joint-venture network shared between Telus & Bell
2 this 800 MHz band is not the same as the cellular 850 MHz band and requires different amplifier equipment
5 both 850 MHz & 1900 MHz are used as needed for voice and/or data now
8 LTE is a high speed data network only, there is no voice call capability (yet)

Voice Band includes: voice calls, standard text messaging, and voicemail notification
Data Band includes: multimedia text messaging, email, and web browsing

Each hardware device is specific to a carrier and is also specific to a network for that carrier. 
The frequency assignments (aka channels) in a given frequency band are unique to each carrier.

There are a number of carrier towers throughout the city, province, and country. For example, Telus has over 450 CDMA towers in Alberta and about 125 in Calgary alone.

Some towers are exclusive to a specific carrier and others are shared by multiple carriers.

Tower height is very important in that a shorter tower will more likely be affected by terrain and obstructions.
Cellular signals will not penetrate or go over hills or metal structures.
(see coverage plot pictures in "getting started")

Antenna placement on a given tower is generally one of two configuration types. The most common type is three antennas placed 120 degrees apart with the first pointing roughly north. The second type is two antennas 180 degrees apart pointing along a road and/or through a valley.