I have had that sort of thing happen on a very weak connection. The connection could be weak due to long distance or due to radio interference from another source such as another AP close by using a close channel, a 2.4 GHz cordless phone or a noisy microwave oven. You can try a higher channel on your AP but I have found that some cordless phones obliterate my connection no matter which channel I use and very strange things start to occur.
I can connect through my Nokia E61 phone using a data plan with T-Mobile.
This just happened in the last week. I had no problems then. I am using the same networks that have worked since my upgrade. I am using OS 2006.
Any clues??? Please???
-F