Why are my call settings disabled (and which settings require operator support and which settings are normally included in service plans)?

As shown in the screenshot below, on my Samsung Galaxy SIII, when I go to Phone -> Call Settings, almost everything is disabled/grayed out. I have a SIM card inside my phone but have not topped up my mobile phone subscription this month. I wonder whether that is the reason why these features are disabled, or whether the reason is that my network provider doesn't support them (after all I am still able to receive incoming calls and SMSs). Is this the case? I would like to use features such as: - placing a call on hold, retrieving a held call, and dialling second (or other) calls - make multipary/conference calls by merging calls - set call diverting (including diverting calls to the voicemail server) - set call barring - set call waiting - set call forwarding - set fixed dialling numbers (FDNs) I wonder which of these features require support for these features from the network operator. I also would like to know whether, and if not then which of these, features are nowadays provided free of charge with a subscription plan from the network operator, and which features normally would not be included and cost extra. Receiving phone calls and SMS messages does not require the account associated with the SIM card to be topped-up (hence is totally free of charge). I know this could vary from network operator to network operator, but due to network operator competitiveness, I would expect most network operator to provide more or less the same features for free as others, and charge for features in case the other operators also do. Thanks. --- EDIT: I've topped up my phone with my pay-as-you-go plan and as a result all of the entries in the above screenshot have become enabled. --- EDIT: Just for the record, I've contacted my network operator. The monthly 10€ pay-as-you-go plan I'm subscribed to happens to include 400 phone hours within the same country, 400 SMS to phone numbers within the same country, 1GB fast Internet followed by unlimited slow Internet. However calls abroad as well as calls to the provider's answering machine service are charged separately/extra. Also, while Caller ID and Call Forwarding/Diverting services are free of charge, Call Waiting will soon incur charges with my provider. I guess other service providers would offer similar service and features at roughly the same price. Regards.