…..put simply, because you have to!
Now, don't get me wrong, there are a thousand reasons for the upgrade, but did you know about this one? There is actually a very serious and technical reason that you should upgrade. I'll try and explain it to you in lay terms….
The current “2G” iphones operate on the GPRS/EDGE Networks (I won't get into the technical stuff, use wikipedia for that). Now you will think that actually that's a good thing, better data usage is good news surely? Well it would be if their was not one simple problem with the 2G network. That is that you cannot use voice and data to the same endpoint (i.e. iphone) at the same time!!! Yes, that's right. You cannot surf and chat simultaneously! Now, this has never really been a problem before a device like the iphone, as most of use would use the data facilities on our nokia or sony so infrequently that we never noticed a problem, however the iphone, being a data hungry beast, is a regular user of data, without your permission!
What this all equates to is simple. If you iphone decides it needs a data connection, say to update its email or something else useful, and at the same time, someone tries to call you, guess what, they don't get through! This kind of defeats the object of the iphone qualifying for the use of the word “phone” IMO!
So whats the answer? simple, upgrade to a 3G phone! this makes use of the new third generation network (HSPA/UTMS), which of course, being data centric, allows simultaneous use of voice and data from a single device.
What more of an excuse do you need to go and get that upgrade?