I have an old Vodafone R205 and previously used it with various SIMs including Spark and 2D. 

The other day I tried to use it with an active 2D SIM and I got a "Limited service" and "No network" error. 

Multiple reboots - no success. Then after a lot of frustration it just connected.

Today I tried again and it wouldn't work initially then randomly did. Tonight it wouldn't connect and then about 10 minutes later - viola it connected.

When I access the settings and try searching network it finds VF, 2D and Spark. When I try to made 2D the preferred network, it wouldn't save the setting.

Any suggestions here please?? Once connected it stays up and works fine!!