Country code +256 (dialed as 00 256 from many places) is Uganda.
Landlines served by UTL all begin with +256 4.
Landlines served by MTN begin with +256 3.
Other landlines begin with +256 20.
Mobile numbers begin with +256 7.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
Gabon is country code +241.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +256 is Uganda, and +256 78 is a mobile.
Mukono Town is in Uganda's telephone area code 041, or +256 41 in international format, the same as Kampala.
Entebbe is in Uganda's telephone area code 042, or +256 42 in international format. Some telephone numbers in Entebbe also use Kampala's area code 041 (+256 41 in international format).
The telephone area code for Bwizibwera, Uganda, is 0485, or +256 485 in international format.
The telephone area code for Gulu, Uganda, is 0471, or +256 471 in international format.
The telephone area code for Hoima, Uganda, is 0465, or +256 465 in international format.
The telephone area code for Kabale, Uganda, is 0486, or +256 486 in international format.
The telephone area code for Lira, Uganda, is 0473, or +256 473 in international format.
The telephone area code for Masaka, Uganda, is 0481, or +256 481 in international format.
The telephone area code for Mbarara, Uganda, is 0485, or +256 485 in international format.
The telephone area code for Mityana, Uganda, is 046, or +256 46 in international format.