Hello...

Leaving for Brussels Monday for a Brugge-Amsterdam-Brussels trip.

I know how to dial Belgian & Netherlands numbers from the USA, but I'm not sure how to dial them within each country and from one country to the other.

(1)(a) How do I dial (32) 50-33-90-51 (Brugge) locally in Brugge?

(1)(b) How do I dial it from elsewhere in Belgium - from Brussels, for instance?

(2)(a) How do I dial (31) 20-624-63-58 (Amsterdam) from Belgium?

(2)(b) How do I dial it from within The Netherlands?

(3)(a) How do I dial (32) 2-219-43-43 (Brussels) from The Netherlands?

(3)(b) How do I dial it locally in Brussels?

Thanks.
SS

1ab. As Belgium uses closed numbering system, you have to use all the numbers preceded by zero wherever in the country you are calling from. So you dial 050 33 90 51. You don't need to dial international prefix 32.
2a. For international call from Belgium, dial 00 + country code + other numbers (often dropping the first zero). So for Amsterdam, dial 00 31 20 624 63 58.
2b. As NL uses open numbering system, you can drop the area code when calling within the same area. So from Amsterdam, you can just dial 624 63 58, and from elsewhere, 020 624 63 58. You can still use 020 from within Amsterdam and still get through.
3a. Dial 00 32 2 219 43 43.
3b. As I've said, dial all the digits preceded by zero - 02 219 43 43.

Are these answers for landlines or mobiles or both? would they apply if I am using a mobile phone with a country code from a third country, e.g. 44?

Usually, with a mobile phone, you use the same code, dialling sequence etc as though you were making the call from your home territory. So to call a local number in Bruge using a mobile phone with a UK SIM, you dial 00 32 50 33 90 51. With some phones/networks, you can dial the local number (without the country code, so 050 33 90 51) and the call gets through. You need to experiment a little. But the first system always works.

With Vodafone you just dial the local number, no need for the country code too on a mobile. It worked fine for me in La Palma this year. However it does no harm to dial the full number. If you are using mobile phone use + instead of 00 before the country code. That will work anywhere in the world - not all countries use 00 to indicate an international call.

In the Netherlands, unless you know you are within an area code area it is safer to dial the full number, with area code, so 020 1234567). Area codes areas are not always logical.
Mobile phones in the Netherlands all start with 06.
There are also premium numbers, 0900 are expensive, especially from a mobile, and should be avoided. 0800 are free, tough you may be charged a connection fee by the mobile provider.