If you are looking to have an Israeli phone number while using your UK SIM card, then Secnum application is the solution.

The secondary number allows you to make calls from your mobile phone using a secondary Israeli mobile number on your existing UK SIM card, regardless of which mobile operator you are subscribed to. The two numbers are on the same mobile phone.

You can use the number to receive SMS messages from other Israeli numbers.

The secondary number provides you with a number you can use to differentiate from your private number.  You can use this number as a registration number to your WhatsApp Business or Telegram.

Outgoing calls are made through the existing American SIM card using your existing mobile phone account according to the agreement you have with the mobile operator.
If you have a plan with unlimited calls then your outgoing calls are included in this agreement. The secondary number is like any regular mobile number that can dial and receive incoming calls to and from Israeli numbers. There is no need to purchase an additional SIM card or another device. The secondary number is activated as a mobile phone application.

Service capabilities:
• Real Israeli Mobile Phone Number
• Dial outgoing calls
• Receive incoming calls
• Send and Receive Text messages
• Set follow me to another number
• Port your own number from another operator
• Personalize ringtone
• Multiple Language UI
• Voicemail 
• Private phone book
• Block anonymous calls
• Advance management Block/Allow callers
• Incoming calls scheduling module allows divert incoming calls to VM, FW number or DND mode, base on working hours

New users get a free trial for 3 days.  If you wish to enjoy premium service, you can purchase it on Google store.

The calls are limited only to Israeli numbers.  It is restricted to dial premium numbers, abroad or to the Palestinian Authority.

An Israeli mobile number on you American SIM card