Phone on the PC will support 10 accounts. The P Series PCs will support nanoSIM? which might have an active and working telephone number. If that is the case, then you can use it for incoming calls. The 10 accounts will be for incoming calls. However, outgoing calls will only use the top 2 accounts. Since you can arrange the accounts around, you can choose to have 2 SIP accounts above the cellular account. In which case, you will receive incoming calls only, and will not be able to make calls with the cellular line. To resolve this, you must set your cellular line to slot 1 or 2.