While playing one expansion, can you get/use skills from another?

I bought the guild wars trilogy on steam and started playing through the Factions expansion as a Warrior, currently lvl 8.

Is it possible for me to acquire bonetti's defense from Prophecies while playing through Factions? How would I do that?

Can I only use Factions skills while playing through Factions?

I checked the map for fast travel to any of the locations that give bonetti's defense but they weren't there.

http://wiki.guildwars.com/wiki/Bonetti's_Defense

also is it possible to travel to prophecy from factions and start doing quests there

*You can use any skills in any campaign you want.
*You can get BD by any method you gain skills in Factions. Buying the skill from a trainer or getting it from a quest will require you to travel to Prophecies and get to the relevant quest giver/skill trainer. This is probably the harder way to do it. A better way would be to unlock it using Balthazar Faction (zaishen challenge is easy, see the link below) and buying a non-elite Warrior tome. You will not need to travel to Prophecies this way.
*http://guildwars.wikia.com/wiki/Balthazar_Faction
*Also, to travel to other campaigns: http://guildwars.wikia.com/wiki/Campaign_Travel

Yes, you can get Bonetti's defense, but there's some work involved:

Step 1: Do enough PvP to gain 1,000 Balthazar faction and unlock Bonetti's Defense at the Priest of Balthazar.

Step 2: Buy a normal Warrior Tome (You can get them for 300-500g) and use that (double click it) on your character to get the skill.

You can only GET factions or core skills in factions territory. You can USE any skills you've obtained anywhere in any of hte campaigns.

Well since I only have one RP character, does this mean I would have to create a PvP character to get BD the Balthazar way?

Will my RP char have access to the skills my PvP char unlocks?

If not I will probably have to do the travel thing.

Do I have to be lvl 20 to buy the skill, and do you know how much it costs?

No. PvE characters can participate in all forms of PvP. Besides, the best way to gain faction for a new player would be Zaishen Challenge, which is a training mission against AI teams. Just travel to the battle isles and you'll be able to play.

Unlocks are account wide. This question is less relevant because you don't need a PvP char to gain faction.

No. There is no such thing as a level restriction for skill use. Afaik, the only time level matters is in certain forms of PvP where you much be under a certain level or must be level 20.

Skill cost depends on how many skills you've bought before. The cost for your first skill starts at something like 10g, and each purchase increases it. It eventually gets to 1k (1000g) and stops increasing. In the long run, it is better to buy tomes (war tomes are about 500g) because they are cheaper.

1: Unlocking a skill is not the same as having the skill. It just means it's easier to get the skill (by using a tome or by buying it from any skill trainer, even ones that normally don't have the skill). You still need to buy the skill (or use a tome). Also note that unlocking skills is account wide and that your heroes (if you have any) can use any unlocked skill.

2: Roleplaying characters can participate in PvP just like PvP only characters, however, they don't have direct access to it. You may need to walk quite far before you can do a specific form of PvP with one (like Fort Aspenwood or Jade quarry).

3: Low level characters can play in low level arenas (if anyone else plays there, of course). One is on Shing jea island chain. I think you get there by talking to an NPC near the xunlai storage area.

U can only do the 4 PvP training matches once with a character.
If u wanna do them again with the same character,
map out after the 3rd match, abandon the quest, and then repeat.

If, like any sane person, you are not interested in PvP, you will need to travel to Prophecies to get the skill. You will need to get to Kaineng Center on the mainland before you can travel to Prophecies.

/agree

1) Gain 1000 Balthazar factions through PvP training matches, then trade your faction points at a Priest of Balthazar to unlock your skill.
2) Buy with your RP character the newly unlocked skill using a regular warrior tome, or complete with a new RP character the pre-searing and acquire the skill at Ascalon city. The skill trainer in Ascalon city is Sir Bertran and he will grant you any non-elìte Prophecies skill previously unlocked through PvP.

Elìte skills can be unlocked with 3000 balthazar factions and acquired only with elìte tomes.

edit:
or, as reported above, complete the Shing Jea quest and mission path, then zone to Kaineng center and from there you may complete this quest to reach Lion's Arch and directly buy your skill without unlocking previously (Firstwatch Sergio sells this skill)

you could also make a prophecies character to unlock the skill (and then delete said character if so desired)...then use a tome to get it on the factions warrior...since you have the trilogy.