I'm Very Glad that You are curious about Shia:
No Circumcision IS NOT NECESSARY for converting to Islam, For converting to Islam you should only believe following:
I testify “Ashhado An La ilaha illa Allah, Ashhado Anna Muhammad'an rasoolu Allah.”
These Arabic words mean, “There is no true god but God (Allah), and Muhammad is the Messenger (Prophet) of God.” Once a person says the Testimony of Faith with conviction and understanding its meaning, then he/she has become a Muslim.
In Shia it is extremely good but not necessary to say after previous testify following testify: "Va Ashhado Anna Allian valyyollah"
which means that I belive "Ali" ( Ali son of Abou Taleb, Mohammad's Cousin) is the one and only true successor of Mohammad (S).
CONGRATULATION! YOU ARE NOW A SHIA MUSLIM :)
sadly. many of unskilled brothers/sisters make it very hard! but reality is converting to Islam is really easy.
Islam is easy to begin but a little hard to master!
After Converting To Islam You should start with 5 main principles (Shia's 5 Pillars):
1.Tohid ( God Is Uniqe -> every thing that we can think of or imagine is NOT Allah, but allah is greater than that. [it needs a little explaination...])
2.Maad (After Life, Heavon and Hell ,...)
3.Nabovvat (Believing Mohammad (S) is Allah Messenger and...)
4.Adl (Justice, Beliving Allah do no evill, do not blame Allah for things we do wrong, we should not blame Allah for anything after all.)
5.Emamat (believing Ali (A) Son of Abu taleb is the real successor of prophet mohammad and after Emam Ali, His Son Emam Hassan, Then Emam Hossein And so on... until 12'th Emam who is alive but hidden from the eye's, waiting for Allah permission to show him self and create a better word) ...
don't move away from these 5 principles. if you can get these 5 principles correctly, then you've done most of the job!
many people, even moslem's underestimates thiese 5 main principles and forget that they are pillars of islam! and everything else such as:
Salat (Praying), Sawm (Fasting), eating Halal Food, even circumcision, and ... are called Ahkam. and Ahkam is come after 5 principles and is not as important as them.
for example, if you don't agree with each of 5 principles, you cant call your self Shia. but if you do not do one of ahkam's rules. then you have done a sin. but you are still a Muslim. for example every Muslim believe that he should pray 5 times each day. but he simply don't! maybe because he is lazy or... he is doing a big sin but he is still a Muslim!.
there is a famous quote from Imam Reza (A) who is Shia's 8th Imam: "Surly The Foundation Of Islam is Tohid and Adl"
=> (Tohid is Pillar number 1 and Adl is number 4)
circumcision is very good thing that every male Muslim is ordered to do. but if one shia do not do it, he have done a sin, but he is still a Shia.
I suggest you not to think about circumcision at first place. shia 5 pillars are faaaaaaaaar more important than any Ahkam like circumcision. after 5 pillars, you should start from most important Ahkam like Praying, Fasting , Taharat, ...
take it easy. god is merciful and he love's you! he'll surly show you the path...
this is my contact email: ArmanBM@Gmail.com
If you have any question about Islam, You can Ask here in stackexchange.com or if it is private you can email me. I would be really happy :)
Fi Ammane Allah. (to be in Allah Protection)