I'm posting mainly to see if anyone else has the same or similar problem. I searched the forum and bugzilla and the closest I found is this bug report: https://bugs.maemo.org/show_bug.cgi?id=10074 .

Recently some strange problems started occuring during connecting to mobile internet via my N900. What happens is:
1. I connect to the internet using 3g
2. Upon connection, the indicator of carrier signal strenght comes from 3g to 3.5g
3. The connection works for some time (it switches to 3g sometimes, but the upon clicking a link or performing some action requiring data download it switches to 3.5g for a moment)
4. Suddenly, the connection switches to 3g and stops working (internet browser doesn't work, ssh connection is closed if I am connected to any remote server, pings from terminal don't work). The N900 still shows the icon that it is connected to the network. The only way to make it working again is to disconnect manually and reconnect (and then the problem usually occurs almost immediately - after downloading one web page for example).

I thought it was maybe the weak battery at first (it was still the original one used all the time since I bought the device in 2009), but after buying new one (decision made after consulting the battery testing thread here on tmo, new battery is enough for 2-3 days of my typical usage) the problem persists. The device runs totally ok if connected on wifi, so I thought then that it is either software problem, modem hardware problem or sim card problem. I moved the sim card to another phone (N95 - it's a bit funny as the guy in bugzilla also used N95 later, but it's irrelevant, just a minor digression) and it worked ok for 2h of constant internet browsing.

I don't want to reflash right now... I'm on CSSU stable with this device and I can live with lack of internet access from it temporarily (I have my shitty old netbook with 3g modem with me most of the time anyway). And I doubt it is the software problem... The logs are pretty clear (I checked syslog mainly - does the modem have its own log or debug interface in the system or anything?)

By the way, as I mentioned, this device is over 4 years old (bought in 2009). I never reflashed this one (I went via all PR and all CSSU stable releases incrementally). The problem started appearing out of the blue this summer.

Can it be similar to the problem when N900 stops recognizing sim cards at all (the one that is caused by faulty simcard socket glueing to the board afaik)?

Any help greatly appreciated