This is free of charge for you as a mobile phone user however, standard call charges per the current minute price list are incurred on the telephone system end for outgoing calls (irrespective of whether or not your mobile plan has a phone flat rate or not!).There are no charges for incoming calls.

For outgoing calls, you as the mobile phone user incur costs (standard call charges for landline calls per current minute price list) for the connection from your mobile phone to the nfon telephone system (irrespective of whether or not the number being called is a landline or a mobile telephone number). These mobile to telephone system call charges can be covered by subscribing to a landline flat rate for your mobile phone, so that you do not incur any additional charges for the call. There are additional call charges on the telephone system end for the connection from the telephone system to the number being called (standard call charges per current minute price list). Incoming calls are free of charge for you as the mobile phone user.If you do not have a WIFI connection and are within the GSM network, charges are incurred for incoming calls on the telephone system end for the connection from the telephone system to your mobile phone (Nvoice Mobile client) (mobile network charges per current minute price list).

If you do not have a landline flat rate for your mobile phone but wish to save the charges for the connection from your mobile phone to the telephone system (standard call charges for a landline call per current minute price list), you can use the “callback” function. When initiating a “callback” from your mobile phone on the GSM network, you are called back by the telephone system, at which time a connection is established to the number being called. I.e., you as the mobile phone user do not incur any call charges. The telephone system however, incurs double the call charges.On the one hand, there are call charges from the telephone system to your mobile phone due to the “callback” (mobile network charges per current minute price list). On the other hand, there are charges on the telephone system end (standard call charges per current minute price list) from the telephone system to the number being called. If you as the mobile phone user have a landline flat rate, using this “callback” function does not make any sense because in this case, there are no charges for the connection to the telephone system. The “callback” function is suitable for mobile phone users without a landline flat rate. This can also optimise call charges abroad (depending on inbound and outbound roaming charges). A “callback” always makes sense abroad if inbound roaming charges + call from nfon telephone system to the mobile phone (Nvoice Mobile) + call from the nfon telephone system to the number being called are less expensive than the outbound roaming charges.

Example: You leave the office and forward calls to your mobile phone (mobile network number). When a call comes into your office number, charges would now be incurred on the telephone system end for forwarding this call (mobile network charges per current minute price list).
If you have a landline flat rate for your mobile phone and want to save the connection charges from the telephone system to the mobile phone, you can use the Nvoice Mobile client with the “reverse callback" function. If the telephone system tries to reach the mobile phone (Nvoice Mobile) for an incoming call, it is a “call waiting” call on the mobile phone. The mobile phone (Nvoice Mobile) then calls the telephone system back and automatically establishes the call. This eliminates forwarding charges on the telephone system end for calls from the telephone system to the mobile phone (Nvoice Mobile) (mobile network charges per current minute price list).  However, the “reverse callback” function only makes sense if you have a landline flat rate for your mobile phone because otherwise, landline charges for the connection from the mobile phone to the telephone system are incurred for each incoming call.