When you talk on a mobile phone, a continuous connection to a channel is reserved for you on the GSM network, which means nobody else can use that channel. With GPRS, you can still have a continuous connection, but you only use the channel when you're sending data.

So, you might be connected to a channel all the time, but you only actually use it when you're sending data. One channel can be shared by many people. This is why you're billed for data transferred, not for time.

GPRS is significantly faster than CSD (Circuit Switched Data, sometimes just called GSM Data). However, you may find transfers slower than the maximum GPRS data rate during peak hours in busy cell networks, because voice connections usually take precedence. The data transfer rate also depends on your device's multislot class, which brings us to the next section.

What Does "Class 10 (4+2, 5)" Mean?

GPRS classes refer to the slots allocated for uploading and downloading data. The class number, in this case 10, signifies the multislot class. The number 4 in (4+2, 5) refers to the maximum number of slots that can be used for downloading - the more slots used, the faster the data transfer. The second number (2) refers to uploading, and the final number (5, which may or may not be shown), refers to the maximum number of slots that can be used at any one time, both uploading and downloading.

So in this case, we could have 4 downloading and 1 uploading (4+1=5), or 3 downloading and 2 uploading (3+2=5), as a slot can only be used for uploading or downloading at one time. However, you couldn't have 2 downloading and 3 uploading, because that would exceed the maximum number of slots for upload.

Here are some common GPRS classes for Nokia phones - but it's not an exhaustive list:

GPRS Class 2 (2+1, 3)
You guessed it, 2 slots for download and 1 for upload. It's a simple class of GPRS that's found in many phones.

GPRS Class 8 (4+1)
Class 8 reserves 4 slots for downloading and 1 for uploading. This is suitable for Web browsing, and also if you read more email than you send.

GPRS Class 10 (4+1, 3+2)
This profile, which is in the example above, is better for back-and-forth use of GPRS, like instant messaging.

EGPRS (EDGE)
EGPRS (Enhanced GPRS or EDGE) uses a slightly different technology based on what's called 8PSK, or 8-Phase Shift Keying . In practice, it makes GPRS transfers about three times faster, and makes downloading larger files like video less frustrating.