I just joined solavei a couple days ago. I chose solavei because of the pricing, and the possibility of my monthly cell phone bill to become non-existent. I was a long time att user, but got sick and tired of the horrible service and outrageous pricing. At 49$ for unlimited everything (data gets throttled at 4 gigs) is a steal imho. The service itself is good, not exceptional, but I do get signal pretty much wherever I go. HSPA+ is a little spotty, but that may be because I have an unlocked att phone (I am currently living in Las Vegas, one of the cities where Tmobile has recently expanded 1900 mHz coverage for HSPA+). I have yet to deal with customer service, and from the looks of it so far, I do not see a need to in the near future. Roaming I have no experience, as I do not roam as much; probably once or twice a year I make road trips.
In conclusion, I do believe that solavei is a great prepaid option, and highly suggest it if Tmobile coverage is good in your area, and have finished your contract, or will be finishing your contract fairly soon (I have about a year left, but ate the ETF, since my savings will more than make up for it in the future).
Disclaimer: I have not used any of the other prepaid options out there, and have no means for comparison, mainly because of solavei's clearly defined data usage policy and that they use GSM technology. However, as stated previously, I have used ATT and do not see much of a difference in coverage; just the large amount of savings that is possible with solavei.
I will NOT be posting my referral site/ID on this forum, so that others who are looking into solavei may run upon this review, and get some objective thought, and no possibility of bias.
Hope this review helps a little, and if anyone has any questions, please do ask, and I will try to answer them as best as I can.