Hmmm...this is a really tough question to answer without knowing 1) who your current provider is and 2) exactly where you are located. I say this because depending on the provider or location, you could be just fine. You could also end up having zero to spotty coverage. It depends on how the network is built. I know, for example, that in NYC (where I live) AT&T uses both the 850MHz and 1900MHz bands/frequencies, but the 850MHz side of the network is better built out and more reliable. It also provides better indoor coverage. In fact, when AT&T launched
3G in NYC it was exclusively on the 1900MHz band/frequency and the coverage sucked;
3G was useless or nonexistent in most places.
3G devices also suffered from poor battery life, because they would constantly search for a
3G signal or switch between 2G/
EDGE and
3G, which also led to many dropped calls.
As to your situation, your phone is strictly 2G/
EDGE so you won't have the exact same problems I had, at least not the switching between 2G/
EDGE and
3G part. You could, however, have a situation where you have poor indoor coverage, spotty coverage, or no coverage at all. A very rare, at least these days, but possible situation is that your phone might not work at all. Again, this depends on your provider. I say this because I remember years ago when I got an unbranded/unlocked tri-band phone (with the exact same bands as yours) and tried to use it on AT&T. It did not work at all. Why? Well, the control channels for the network were on the 850MHz band/frequency and my phone did not support that band. I believe in most cases the control channels are on both bands/frequencies, so that might not be a problem at all.
Most important, though, it depends on the provider and area and how well the 1900MHz side of the network is built. If it is just there for capacity issues and the 850MHz band/frequency is what's mostly used, then you could have serious issues in regard to service. All that being said, you might have no trouble at all. As a last point, there are quad-band phones you could buy or have bought that would alleviate all this. A quad-band phone supports all
GSM/2G/
EDGE bands that are used throughout the world, so you would have no problems, no matter where you used it. Nokia sells many quad-band phones. I'm using one right now and have used several throughout the years.
I do have three questions:
1) Why would buy a phone knowing that it might not work well? As you mentioned, the network is 850MHz and 1900MHz, so you made a conscious decision to buy a phone that potentially supports half the network.
2) Are you still in contract with your current provider? I ask because if you are, then switching to another provider will cost you an early termination fee. I don't know the provider, so I cannot say how much.
3) Why all the secrecy? If you want the best help, you have to help us to help you. Naming your provider and general location or even the other provider will not lead us to come over for dinner.