I know this is too late to post as Dell Venue is complete extinct in market but still i know many people own this device and love it
SIM card issue, Suddenly this phone pops up that SIM card is not inserted or unavailable, Network go away and automatically get resolved after restart or after re assembling battery.
Many people believe that this issue is happening because they loaded a custom ROM on device and THIS IS NOT CORRECT.
I own Dell Venue and facing this issue from last 8-9 months. I tried MIUI, CM7 various version but issue was always same..
Some people think its a network IC issue, That is wrong because phone can still show you available networks.
Dell Device motherboard doesn't have all the component soldered on it and they are just assembled in such a way that it stay in physical contact with motherboard, SIM card holder is one of them. SIM card holder is a small PCB placed over motherboard and pushed against motherboard with the help of its case. Once your phone is few months old or fell down several times, The body of phone becomes slightly loose and cause the issue that SIM card holder lose contact from main motherboard and phone pops that SIM card issue.
1. UNSCREW your phone. There are 5 screws on phone. 4 are visible and 1 is under a white cap.
2. Open the case. Be CAREFUL of its small component and antennas
3. You will get SIM holder, Flash and antenna completely out of motherboard.
4. Now you will find all these components are connected to motherboard by golden colored metal (Like battery contact metals in every phone).
5. Use a pin and push all those metals litle out (like you used to do in your nokia phone when your battery used to loose contact with phone)
6. Clean all the component safely (Optional) - But i did because there was a lot of dust got collected in case causing it to get loose.
7. Assemble your phone back and tight the screws really well.
Turn on the phone and your phone is new again.
These steps will resolved WIFI and network issues as Antennas of phone are also connected in same way.
NOTE. Antennas are tiny metal plates placed under side silver plastic case. DO place them back else WIFI and GSM will show very low network.
I did this two weeks back and not a single time i got sim issue again, moreover my WIFI and GSM range is improved.
Hope this will help.